AirShaper

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In this video we’ll explain flow separation (or boundary layer separation).
In our previous video on boundary layers, we saw that the air close to the surface will stick to it, forming a boundary layer. But in some cases, it can become too difficult for the air to follow the curvature of the surface, causing it to detach. Let’s have a look at why this can happen.

When you look at air flowing across a flat plate, as in our previous video, the free stream velocity remains constant. Because of Bernoulli’s equation, which states that pressure changes with velocity, this means the pressure gradient in the X-direction is more or less to zero. Also, the pressure is imposed onto the boundary layer and so doesn’t really change much in the direction perpendicular to the surface either. That means the pressure gradient in both the x and y direction are close to zero.

But when the air flows around a curved surface, it speeds up and slows down. Take the flow around a cylinder for example: at the front, the pressure is the highest as the air comes to a complete standstill – this is the stagnation point. As the air then curves around the cylinder, it speeds up and this creates a drop in pressure. As the pressure goes down with increasing x, this is a negative pressure gradient, which is good: the air is being pushed downstream, overcoming the friction in the boundary layer, which gradually builds up.

The maximum velocity is reached somewhere around the midpoint of the cylinder, after which the air starts to slow down again. This means the pressure gradient is now reversed: as the air travels across the surface, the pressure goes up. This is what is called an “adverse” pressure gradient and the air is no longer driven but obstructed by the pressure difference: it has to flow into regions with higher pressure.

If the pressure gradient is positive or zero, as in the case of the flat plate, then the velocity gradient perpendicular to the wall is positive: the further you move away from the wall, the higher the velocity. But when the air travels against an adverse pressure gradient, the velocity profile is pushed back and this reduces the velocity gradient at the wall.

At some point, the velocity gradient becomes zero, which is the point where the flow separates or detaches. Beyond this point, the velocity profile is zero both at the wall, because of the no-slip condition, and at the inflection point, which is where the velocity crosses from negative into positive. In the negative velocity region, between the surface and the inflection point, the air flows in a direction opposite to the main flow  – this is called a recirculation. The separated flow will now surf on top of this recirculation flow and the boundary layer and wake will continue to grow, which can have a negative effect on drag.

In reality, shapes can be much more complex than cylinders and flows can detach and reattach in various locations. Even on a smooth wing, the flow can detach and reattach. So, this is very much a 3-dimensional challenge and getting it right requires a careful analysis and optimization of local and global pressure gradients.

Also, keep in mind that flow separation can happen in both laminar and turbulent boundary layers. Turbulent boundary layers, however, carry more momentum and will typically stay attached to the surface further downstream compared to a laminar one – just check our video on golf ball dimples or vortex generators to learn more.

Flow Separation - Boundary layer separation explained

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In this video, we explain what a boundary layer is.

Let’s look at two extremes first:
No-slip condition: no matter how smooth the surface is, the flow will always stick to it, having a flow velocity of zero on the surface of the object.
Free stream velocity: the velocity of the undisturbed air, far away from the object

To understand what happens in between these two extremes, let’s look at air flowing across a flat plate. As the undisturbed air meets the leading edge of the plate, it will locally stick to it because of the no-slip condition. As the air moves or slides across the plate, this layer or air sticking to it will grow thicker. This region, where the air moves slower than the free stream velocity, is called the boundary layer and it is mainly determined by the viscous forces. Outside of the boundary layer, the viscous forces are much less important and sometimes even ignored in fluid modeling

You can have a laminar boundary layer, with layers of air moving parallel to the surface, or a turbulent boundary layer, filled with vortices featuring velocity variations in all directions.
If the incoming airflow is laminar itself and if there are no disturbances that can trip the flow, the boundary layer will start off as laminar. As the air continues to move along the plate, so does the distance traveled from the leading edge. If we use this distance to calculate the Reynolds number, it’s clear that the Reynolds number will continue to rise as we move further down the plate. 

When the Reynolds number crosses a critical value, which can be different for each application or geometry, the laminar boundary layer will start to transition into a turbulent one. The velocity profile of both types is very different and can have a large impact on the total friction & pressure force on the object.

In applications like airplanes, where shapes are smooth and streamlined, the goal is to maintain a laminar boundary layer as long as possible: a turbulent boundary layer increases the friction drag and typically is thicker than a laminar one, which increases the effective thickness and thus the pressure drag of the wing.

In applications with less streamlined shapes, like sports athletes or golf balls, it can be beneficial to trip the boundary layer and make it turbulent: turbulent boundary layers carry more momentum and will push the separation point further downstream – that’s the reason golf balls have dimples and athletes wear special suits or even shin tape, reducing the wake they leave behind.

What is a Boundary Layer - Laminar and Turbulent boundary layers explained

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In this video, we'll explain the aerodynamics behind curved free kicks, corners, and so on! Want to bend it like Beckham? Then stay tuned!

Soccer aerodynamics - How to curve a ball

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In this second video on the Porsche Taycan Aerodynamics, we’ll take the car to the street to compare tuft movement to simulation data.
Special thanks to the Porsche Centre in Mechelen, Belgium, for letting us play with this fantastic car 😊
https://www.porsche.com/belgium-mechelen

In our last video, we had equipped the Porsche Taycan with a number of tuft

Rear window & spoiler

On the rear window and spoiler, none of the tufts move. This is because the flow in that area stays nicely attached & laminar. There is some slow-down of the flow due to the “negative” curvature of the window, but this doesn’t lead to separation.

Rear wheels
The rear wheels create a turbulent zone which extends downwind (causing a lot of movement of the tufts on the rear bumper) and also upward (creating movement above the wheel arch as well). The latter extends all the way to the rear spoiler.

A-pillar and side window
As the air makes its way from the front wind shield to the side window, it curves around the A-pillar. In doing so, a vortex is created which locally pushes the air upward, just behind the A-pillar. This upward motion extends further downwind at the top of the side window as well.

Front wheels
The front wheels also create a turbulent zone which splashes out upward. Further downstream, this zone is countered by the air coming off the front hood, which creates a zone of attached air curving downward on the flanks.

Headlamps
The headlamps are located in a “pocket” in the bodywork. As the air jumps out of this pocket, it locally separates from the bodywork and leaves behind a local bubble of separated, turbulent flow. This can be seen in both simulation & tuft movement.

Porsche Taycan Aerodynamics Part 2: Road testing

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In this video, we will go over the aerodynamic features of the Porsche Taycan and prepare it for road testing! Special thanks to the Porsche Centre in Mechelen, Belgium, for letting us play with this fantastic car 😊
https://www.porsche.com/belgium-mechelen

In our last video, we had optimized the rear of the Porsche Taycan using our Aerodynamic Shape Optimization technique (to have it generate more downforce), In this video, we get up close with all the other special features of this car (underfloor, diffuser, wheels, …)


Underfloor

At the front splitter, the air jumps underneath the car and accelerates as it gets into the channel formed by the road surface and the underfloor of the car. This increased velocity will reduce the pressure, creating a suction force pulling the car downward (which is good for handling).
On electric cars, the underfloor can be made very smooth & flat, as it sits below the battery pack and as they have very little exposed components. So the air maintain its velocity and connect with the diffuser at the rear, where it connects to the wake behind the car, reducing drag, increasing downforce and so on.


Wheels
Wheels are a major source of aerodynamic drag on cars. They are large, unshielded elements rotating through the air, acting like a mixer. Not only do they generate drag themselves, they also create turbulent air downstream, which can increase drag / reduce performance elsewhere.

Porsche has fitted the car with air curtains, which are channels in the front bumper. The opening at the front accepts the high pressure are at the nose of the car which is then sped up to exit at high velocity through a slot at the rear of the front bumper, just ahead of the front wheel. This creates a curtain, shielding the turbulent air coming off the rotating wheel.

Another feature are the aerodynamic rims. To limit their drag, they created a rim which is more “covered” than a regular rim. Secondly, the profile of the spokes has been designed in such a way that the air nicely slides across the spokes, instead of being pushed away by more blunt spoke shapes.

And finally, Porsche also air deflectors in front of the wheels: these are small “ramps” that divert the air so it doesn’t hit the wheels directly (where it would create a large wake). These are present both at the front & the rear wheels.


Rear spoiler
The active rear spoiler will automatically extend when you are going fast enough to improve downforce & aero balance of the car.


Coolers
Air is forced through the coolers and this represents an energy loss. So when you don’t need full cooling power, it’s good for efficiency to (partially or fully) close the entrance to the coolers. This will reduce the energy lost on air going through the coolers and will make the air go around the car instead.


Ride height
The Porsche Taycan has an extremely low drag coefficient of 0.22 and one of the tricks to achieve this is to lower the ride height of the car. Lowering the ride height at low speeds would be impractical towards ground clearance, speed bumps etc, so it is lowered dynamically as the car picks up speed. A lower ride height also has a positive impact on the handling of the car, as downforce typically increases with reduced ride height.


Tufts
We equipped the car with tufts, which are small strands of wool that will align themselves with the local orientation of the airflow. This allows us to analyse flow patterns and see where the air has detached and/or has become turbulent.


Next video
Stay tuned for our next video, where we’ll take the car for a ride and compare the tuft patterns with what we saw in simulations!

Porsche Taycan Aerodynamics Part 1: aero features explained

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Pitot tubes are small devices used on aircraft, turbo machinery and even Formula One cars to measure flow velocity, or rather, measure pressure to calculate flow velocity.

Basic theory
The Bernoulli stated that the pressure goes gown as the velocity goes up, when following a particle along its flow path. For incompressible fluids, this can be stated using the following equation:

P_static + 0.5*rho*v² = P_total

P_static: this is the static pressure, which is the pressure you would feel when traveling along with the flow without disturbing it.
0.5*rho*v²: this is the dynamic pressure, which basically relates to the kinetic energy of the fluid.
P_total: this is the total pressure, which is the pressure you would measure when you bring the flow to a complete standstill – therefore, it’s also called the stagnation pressure.

The interesting thing about this equation is that we can reshuffle it to calculate the velocity based on the static pressure and total pressure:
V = sqrt( (2*(P_total-P_static) ) / (rho) )


Measurement probes
So how do we measure the static and total pressure? Well, you guessed it – we can use a pitot tube!
At the front of the pitot tube, which points directly into the wind, the air comes to a complete standstill. This means that the pressure measured there equals the total pressure.
At the side of the pitot tube, the openings are parallel to the flow and so it is not slowed down. A “static ring” as it is called is often used in these kinds of probes.  The pressure measured here equals the static pressure.

Logging the pressure difference
The next step is to obtain the difference between the static pressure and the total pressure to calculate the dynamic pressure. You can do this in an analogue way, by connecting both tubes coming from the measurement openings to a manometer or a membrane. The difference in water height or membrane deflection can then be used to calculate the pressure delta and then the velocity. Or you can hook the tubes to a pressure transducer and use the electric output signal to log the data.

Limitations
Keep in mind that a pitot tube can only measure the relative wind speed, so the difference in velocity between the object and the air (called the airspeed in aviation terms). So if you want to know the absolute speed of your object versus the real world (called the ground speed in aviation), you’ll also need to measure the velocity of the wind itself. Or cheat, and use your GPS 😊
Also important is to keep the pitot tube pointing straight into the wind, although more advanced versions are able to measure not just wind speed but also the angle of attack of the wind. –7
Pitot tubes come in various shapes and forms, like this elbow version I got from the lovely Katharina Kreitz of Vectoflow – they actually make pitot tubes using 3D laser sintering to create complex internal channels for custom applications.

Use in applications
Pitot tubes are used in countless applications. Airplanes are the most obvious, where they log the airspeed. But they are also used on the front of Formula One cars, to have a good reference velocity to compare to wind tunnel data. They’re also key to measure & calibrate the wind speed of wind tunnels, just ahead of the test section. And I’ve been told pitot tubes have even been used to measure the airflow in kitchen cooker hoods – not kidding you!

Pitot Tubes - Measuring Flow Velocity

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In this video, we'll discuss Aerodynamic Shape Optimization using the adjoint technique.

General optimization problems
Imagine we want to maximize a certain output value Y (like airfoil lif) by changing the input variable X (like the angle of attack). The relationship between both can be expressed through a mathematical function, which we'll call the objective function.

To find the maximum lift value, we can pick a random angle of attack value on the X-axis and then calculate the corresponding lift value on the Y-axis. We can then pick a second point close to it and do the same thing. With these two data points known, we can calculate the local gradient, which indicates the direction in which we need to march to get closer to the maximum.

After enough steps, you will have reached the maximum. The downsides of this technique are that you can miss the peak or get stuck on a local peak, but this is the general procedure used in gradient-based optimization techniques.


Aerodynamic Optimization
In aerodynamic simulations, the airflow around an object is chopped up in small pieces called cells within a mesh. The surface of the object is also chopped up into small pieces called surface cells with nodes on the corners.

To obtain the total drag or lift of the object, we need to integrate the pressure & friction forces on all these local surface cells to get the total value. This indicates that the position of each individual node has an influence on the final drag & lift on the object.

The objective function, therefore, has thousands if not millions of input variables: the X, Y and Z coordinate of each individual node. To obtain the local gradient, you would need to move one node individually and then re-run the entire calculation to calculate the local gradient. With that information, you know whether to push the node inward or outward to increase or decrease the objective function. Once you have obtained all these local gradients, you can put them together into what is called a surface sensitivity map.

As you can imagine, re-running the entire simulation for each node displacement can become very expensive. Luckily, there is something called the adjoint technique.

Adjoint
The adjoint technique allows you to calculate all of these local gradients, or sensitivities, in one single simulation. Here's how this works:

- Normal aerodynamic simulation (primal or forward simulation):
After the computational mesh has been generated, the flow field is typically initialized using a fixed value (zero or something else). Then, the properties defined at the boundary conditions (like an inlet flow velocity for a virtual wind tunnel) propagate through the domain. After enough small time steps, the solution will have converged to a stable flow field.

- Adjoint simulation (dual or backward simulation)
Starting from the aerodynamic simulation data, the adjoint simulation will take small "time" steps. It calculates backward from the objective function to see how each node position affects this objective function. Based on these results, we can then calculate all the local gradients and construct the sensitivity map.

So instead of running a full aerodynamic simulation for each local gradient calculation, which would be prohibitively expensive, we can now calculate all the gradients with just two simulations: the normal (primal) and the adjoint (dual) simulation.

Morphing
The next step is to use the input of the sensitivity map and start implementing it: move the surface inward or outward based on what the map tells you. Once you have morphed the 3D object, you can re-run the aerodynamic simulation to see how much the objective value has changed. You can then also re-run the adjoint simulation to create a new sensitivity map and to the morphing again.

With each cycle, you will get closer to the most optimal shape for your object. You can do this for the entire object or you can define a design space in which the algorithm can operate.

Porsche Taycan
Interestingly enough, the adjoint optimization technique - when asked to increase downforce - starts to create the iconic ducktail spoiler that Porsche has been applying for years.

For more information or to run your own optimization project, just contact AirShaper at info@airshaper.com


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The adjoint code used is part of OpenFOAM v2012 and was developed by the Parallel CFD & Optimization Unit of the National Technical University of Athens (http://velos0.ltt.mech.ntua.gr/research/index.html). Details about the theoretical background of the adjoint method can be found in the publications listed here:
http://velos0.ltt.mech.ntua.gr/research/pubs.html

Aerodynamic Shape Optimization - The Adjoint CFD Method

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How to use coastdown testing for drag measurement

What is coastdown testing?
A coastdown test is one of the most common tests in the automotive industry. It is a way of measuring the mechanical and aerodynamic resistance that acts on a vehicle. 
The vehicle is accelerated to a particular speed and once constant, the clutch is engaged. The vehicle is then allowed to slow or ‘coast’ down in neutral. By recording the distance travelled and the time taken, the aerodynamic drag can be calculated (see also: https://airshaper.com/videos/what-is-aerodynamic-drag/video/DbIIw-WryHY)

How to calculate the drag coefficient
See also: https://airshaper.com/videos/what-is-a-drag-coefficient/video/bEgoZ_dAg7o
For simplicity, let’s assume the vehicle is slowed down by only two forces: 1) mechanical resistance and 2) aerodynamic resistance. Mechanical resistance is primarily due to the rolling resistance of the tyres and therefore remains constant, regardless of the vehicle’s velocity. Whereas aerodynamic resistance changes with the square of speed. In other words, drag force has less of an affect at low speeds, but a large affect at high speeds.

Newtons 2nd law states that the acceleration of an object is directionally proportional to the sum of the forces acting on it. Applying this to our simplified coastdown test, we get an equation which includes a rolling resistance coefficient, Crr and a drag coefficient, Cd.
So how do you calculate the value of two coefficients from a single equation with only one measurement? First, let’s look at two extremes:

1)   No aerodynamic resistance
If the vehicle completed a coastdown test in a vacuum, where there was no air resistance, then only the mechanical resistance would slow it down. Therefore, the car would decelerate at a constant rate, resulting in a linear deceleration curve.

2)   No mechanical resistance
If the vehicle had no rolling resistance and so only the aerodynamic resistance was slowing it down, then the deceleration curve would be non-linear. The car would decelerate faster at high velocity and slower at low velocity.

In reality, the measured curve from your coastdown test would be a combination of both. You can then adjust the coefficients to alter the shape of the curve until the measured curve matches the predicted curve. This process is called least squares regression. Overall, you will end up with a value for aerodynamic drag and a value for mechanical resistance.

As ever in aerodynamics, it is unfortunately not that easy. In reality, the equations mentioned above are much more complex. They need to account for factors such as mechanical resistance in the drivetrain, ambient conditions, wind direction, gravitational force and rotational inertia.

Yet, despite its complexity, coastdown tests are an industry standard for determining the performance of a vehicle. So, if you want to find out the drag coefficient of your car, why not use your cell phone’s GPS and some Excel magic to conduct your own coastdown test?

Drag Measurement  - Coastdown Testing

How to use coastdown testing for drag measurement

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In this third video in our series "How Wind Tunnels Work" we look at wind tunnel measurement techniques - both some of the most widely used as well as some innovative ones.

Forces & moments
One of the most important output parameters of a wind tunnel test are the forces & moments on the object. To obtain these, the object is typically connected to a 3D force balance, which is a device that can measure the forces and moments around three perpendicular axes.

It's important to make sure that the influence of the connection part does not disturb the airflow too much, which is why they're often given an aerodynamic profile.

Surface pressure measurement
To measure the static pressure on the surface, you can use pressure taps. These are small holes drilled perpendicularly to the surface with a tube fitted to each hole in the model. These tubes are then sent to a pressure transducer which is typically located outside the wind tunnel, where the pressures are measured & logged.

If you want to measure the pressure on many locations on the surface of your object, you'll quickly end up with a huge set of cables that needs to be led outside. This is something you need to take into account during the design of your prototype.

Alternatively, you can work with miniaturized pressure transducers that fit within your model and then convert the measurements into digital data which is then sent to the outside world via a single cable to save space.

3D flow measurement
- Smoke: one of the oldest & most common techniques is to release smoke upstream of the object to trace the path of the air. This can lead to very insightful information in terms of where the separation point is located, what the size is of certain vortex structures and so on. But it's quite difficult to determine local flow velocities, so over the years, a number of alternatives have been developed.
- PIV - particle image velocimetry: tracer particles are released upstream of the area of interest. The size, density, ... of these particles are chosen in such a way that they follow the real flow nicely, without dropping to the ground or disturbing the flow pattern. They are then illuminated, typically in a 2D plane, using a laser. Then, they're filmed perpendicularly to that plane by high-speed cameras. By tracking & tracing the position of the individual particles between consecutive shots, one can reconstruct their path and calculate the velocity vector and flow field.
- 3D measurement probes: by measuring the differential pressures at the head of these multi-hole probes, you can obtain the static pressure and total pressure, the angle of attack and the velocity. If you then trace the position of the probe itself in 3D, you can reconstruct a 3D flow field.

How Wind tunnels Work - Measurement techniques, PIV, pressure taps, force balance, pressure probe.

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In this video, we explain the huge variations in size, speed and accuracy of low-speed aerodynamic wind tunnels. This is mainly due to variations in:
- object size
- object velocity
- required accuracy


Object size
When you place an object in the wind tunnel, the air needs to curve around it and fit between the object and the walls of the wind tunnel. This creates 2 problems:
- Blockage ratio: around the object, the cross-section through which the air can flow is reduced. This means the air will locally speed up compared to the reference velocity, which is typically set at the undisturbed beginning of the tunnel using a pitot tube.
To compensate for this, you can calculate the blockage factor. Typically, it's recommended to keep this value below 5-10%.
- Wall effects: a boundary layer of slower moving air is present close to the wall. In reality, this slower moving air is usually not present and can bias the results. Also, the walls can interfere with the flow & pressure patterns around the object if they're too close. In that regard, it can be very interesting to first run a CFD simulation to analyse the flow and see exactly how large this "zone of disturbed air" is to know how far it should form the walls. One example are the vortex structures around wingtips.

In some cases, you'll even see wind tunnels employing an open test section, partially to overcome the challenges of blockage ratio & wall effects.


Object speed
The velocity of the application can vary greatly, with a cyclist going 10 m/s and an airplane 250 m/s. Ideally, you select a wind tunnel with the wind speed that you need. In reality, there will be 2 main constraints:
- Budget: an automotive tunnel can easily cost 5.000€ per hour. Building one also costs over 100 million euros in some cases.
- Availability: tunnels are often overbooked and sometimes they just don't exist in the size/speed combination that you need.

Scaled model testing can help in that case. But keep in mind that you'll need to respect certain similarity numbers - the most important one being the Reynolds number. If you want to keep the Reynolds the number the same when scaling down your model by a factor X (so length_scaled = length_full / X), then you need to scale up the velocity by that same factor X (so velocity_scaled = velocity_full * X). This can make you hit the speed limit or the wind tunnel or even the limit of compressible flow (around Mach 0.3).


Accuracy
The higher the flow quality or the more realistic the setup needs to be, the more tricks you need to pull, like cooling the air, working with a moving ground or even employing gases other than air at different pressures / temperatures.

How Wind tunnels Work – Blockage factor, wall effects, scaled model, similarity number, moving floor

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In this first video of our series on wind tunnels, we’ll discuss the basic layout.

History
Wind tunnels were invented in the late 19th century and even the Wright Brothers used a simple wind tunnel to study different shapes for their Wright Flyer, the first plane. The principle of a wind tunnel is quite simple: Use a single or multiple fans to force air across an object to study its aerodynamic properties.

Layout
In an open return tunnel, the air is drawn from the environment in which the tunnel is located. This type of wind tunnel is typically cheaper to construct and doesn’t suffer too much from smoke or exhaust gases accumulating inside. It is however quite expensive to operate, as it constantly needs to accelerate “new” air from standstill. It’s also more challenging to achieve a good flow quality as the air needs to curve into the inlet. And the open exit makes it quite noisy as well.

Then there’s the closed return tunnel, in which the exit air is fed back to the inlet. This design is much more energy efficient as the fan only needs to overcome the losses and it’s quieter too and it has the potential for a higher flow quality. Downsides are a higher construction cost and because the air circulates, it can heat up quite a lot and smoke & exhaust gases can accumulate.

Goals
Whichever return type you go for, it’s very important to have good flow characteristics at the test section. Typically, the goal is to have a low turbulence intensity, a uniform flow velocity and a thin boundary layer.

Components
Let’s have a look at how the typical components of a tunnel are set up to achieve this: first, the fan pushes the air forward. Then, in the corners, turning vanes are added to help straighten the flow and reduce pressure losses.

After the last corner, the air hits the settling chamber, where it first passes through a honeycomb structure. This is basically a set of tubes to force the air to move in a parallel way to reduce the swirl. After exiting the honeycomb, the air goes through a number of screens, which are composed of thin wires interwoven to form square or rectangular meshes. These screens impose a static pressure drop which is proportional to the velocity squared, penalizing speeds above average and boosting speeds below average. This helps to reduce variations in longitudinal flow velocity. They also break up large eddeys into smaller ones, which decay faster.


To reduce the pressure drop in the entire circuit and settling chamber, the cross-section is quite large and thus the flow velocity relatively low. To speed up the air and further improve flow uniformity, after the settling chamber the air is then sent through a contraction just before it enters the test section. After the test section, it is slowed down again in the expanding diffuser before it enters the fan again.


So that was it for our first video on how a wind tunnel works. Stay tuned for more as we discuss sizing challenges and measurement techniques!

How Wind tunnels Work – Contraction, Test Section, Diffuser, Fan, Turning Vanes and Settling Chamber

CORRECTION (0:57 to 1:30) for the picture on the right-hand side: 'laminar boundary layer' should be 'turbulent boundary layer'.

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In this video, we look at the aerodynamics of golf ball dimples and how to apply (or not apply) them to your design!

Aerodynamics of a sphere
A golf ball without dimples, a simple sphere, features attached, laminar flow at the front: as the air moves over the surface,  a boundary layer of slower moving air grows thicker as it sticks to this surface. As soon as the flow goes beyond the halfway point and needs to contract, it becomes more & more difficult for the flow to stay attached to the surface and eventually. Separates, resulting in a detached flow. This creates a large wake behind the golf ball, which increases drag and slows it down.

Aerodynamics of a golf ball with dimples
When you apply dimples to the surface, the boundary layer becomes turbulent. It will mix with the surrounding air and retain more kinetic energy. This energy allows the airflow to stay attached further down the back of the golf ball, moving the separation location further downstream to reduce the size of the wake. These dimples may increase the friction drag a little but reduce the pressure drag so much that the golf flies roughly twice as far!

Golf ball dimples on cars, golf ball dimples on planes, ...
So does this mean we should cover every surface on every car or plane with dimples to make it more aerodynamic? No, not quite. It only makes sense to create a turbulent boundary layer just ahead of a separation location. Modern day cars for example, have such a sleek profile that they have attached flow all the way to the back of the car. And even at the back of the car, a turbulent boundary layer would still not be enough to make it follow the negative curvature at the end of the trunk.

Golf ball dimples in sports
Another example is to reduce drag around cylinders. There it does make sense, depending on the Reynolds number, to add roughness or dimples or what so ever, to move the separation location further downstream. But on a golf ball you have dimples everywhere because you don’t know the direction of the golf ball. On a cylinder, if the flow is coming always from the same direction, it makes sense to only add roughness just ahead of the separation location, so not at the rear of the cylinder where the flow is already detached. A practical example of this are the arms of an athlete or cyclist, where the wind always comes from the front or a slight angle of attack, so it makes sense to only add roughness just ahead of the separation location on the arms. This is something you already see on some outfits of the riders.

Golf Ball Dimples Aerodynamics - How do they work and are they relevant for your design?

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Full Research Paper: https://www.airshaper.com/research
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In this video, we look at how machine learning / deep learning / neural networks can be applied to aerodynamic CFD simulations.

Neural Concept
We interviewed Pierre Baqué, CEO of Neural Concept, a Swiss startup developing & offering Deep Learning software. They have developed algorithms to connect 3D shape morphing, deep learning and aerodynamics.

senseFly
senseFly is a Swiss drone company that wanted to improve the flight time of their fixed-wing drones. senseFly, Neural Concept, EPFL (the technical University of Lausanne - École polytechnique fédérale de Lausanne) and AirShaper teamed up to apply Deep Learning to drone design to improve the aerodynamics, as improvements to the lift/drag ratio directly extend the range / increase flight time.

Deep Learning setup
The Neural Concept software can create & explore new 3D shapes to train its network, but it needs an aerodynamics component to give feedback on the lift/drag performance (and other aerodynamic parameters) of each design. For that, the Neural Concept software connected to the AirShaper cloud via an API interface.

Network Training
The training of the network was done in multiple phases with increasing accuracy. The initial warm-up of the network was done using older, in-house simulations from other projects. In the second phase, medium accuracy AirShaper simulations were applied. And in the final phase, high-accuracy AirShaper simulations were used for final tweaking of the network.

Output
Without any design input, the network came up with special drone shapes that partially matched what engineers had been applying for years in practice (anhedral/dihedral setup, ...). The lift/drag ratio was improved by more than 4%. Because the Reynolds number is quite different compared to large aircraft, so were the suggested design solutions.

AIRBUS
Neural Concept worked on the prediction of shock waves (transonic simulations). These results were presented at NEURIPS.

Future of Deep Learning for Aerodynamics
- Today
For industry specific, repetitive tasks, it pays off to train a network so that new designs can be analysed using the predictive model
- Short term
In the short term, machine learning can be used to make existing CFD codes faster and more accurate
- Long term
It's uncertain if it will ever work, but it might be possible to create generic Neural Networks that cover various industry segments, without needing to train the network.

Machine Learning for Aerodynamics - Deep Learning & Neural Networks applied to CFD simulations

For more information, visit https://www.airshaper.com or email info@airshaper.com
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To understand the advanced aerodynamics behind the T50, let’s travel back into time to some of Gordon Murray’s most famous creations.


Legendary cars by Gordon Murray
---------------------------------------------
Brabham BT46
Inspired by the ground-effect Lotus Type 78 featuring side skirts and the Chaparral 2J “sucker car”, featuring 2 fans at the rear, Gordon Murray and the team installed a massive fan at the rear of the Brabham Formula One car. Because ‘moveable aerodynamic devices’ were not allowed, its official purpose was actually to improve cooling, which it did. What it unofficially also did, was to draw air from underneath the car. With side skirts around the car closing off the underfloor area from the outside air, the fan was able to maintain a low pressure underneath the car. This led to high amounts of downforce, enabling crazy cornering speeds.

McLaren F1
On sports cars, you’ll often see a diffuser, the upward sloped rear part of the underfloor. It’s there to increase the airspeed underneath the car, which will help to create suction because of the Bernoulli effect. If the upward angle is too aggressive, the air will not be able to follow the curvature and will continue on its own, more horizontal path. This is what we call a “stalled” diffuser. To activate it and make the air follow the curvature, the fans draw air away at the beginning of the diffuser step. This helps to remove the boundary layer and makes the airflow stick to the underfloor surface. It increased downforce by 5% and reduced drag by 2%.

Aerodynamic analysis of the Gordon Murray T50
----------------------------------------------------------------
Fan
The fan has an 8.5kW electric motor and can spin up to 7.000 rpm. It will eject the air into the wake behind the car, helping to reduce drag by virtually creating a long-tail car. And the 15kg of thrust it produces is around 2.5% of the total drag on the car, so that effect is actually significant as well. Even more so – from what we understand from various interviews, it’s actually more efficient to provide 8.5kW to the fan and not to the drive shafts to increase top speed. Now let’s see how the fan works together with other parts of the car in different aero modes. 

Downforce mode
In down force mode, the fan will source air from the diffuser channels. The car has 2 very pronounced diffuser channels which fit between the engine bay and the rear wheels. They are so high that the exhaust system of the engine was actually moved upward to make room for them! Another consequence is that the suspension arms and even the drive shafts need to cross the diffuser channels to get to the wheels. That’s why the suspension arms have been given an aerodynamic profile, just like in formula One and Indycar, to limit their impact on the airflow.
On the official CFD, or computational fluid dynamics, images we can again see an aggressive step at the beginning of the diffuser, similar to the one we saw on the McLaren F1. Without fan assistance, the air is not able to follow this profile and the diffuser stalls, creating just a mild diffuser effect. But in downforce mode, the fan draws its air from the beginning of the diffuser, at the steep part of the step. This helps to remove the boundary layer and to make the air to stick to the profile. This not only creates downforce at the rear, it also helps to accelerate the air underneath the entire car, creating down force at the center and front of the car as well. That eliminates the need for a big splitter at the nose to correct the aero balance, which is the split between downforce at the front and rear. Also in downforce mode, the aerofoils or flaps at the rear of the car tilt upward. In total, down force mode will generate 50% more overall downforce on the car.

Streamline mode
The rear spoilers drop by 10° to reduce base suction, which is the pressure just behind the car, holding it back. And the fan will now source its air from the top air inlets. This again helps to remove the boundary layer which will help to reduce drag on the parts downstream of these inlets. Together with the virtual long-tail effect, drag is reduced by an impressive 12.5% in streamline mode.

Vmax mode
This is basically the same as streamline mode, but the fan is now powered by the battery instead of the engine, to free up engine power.

Brake mode
The flaps rise even further to their maximum angle of 45°. This mode provides a 100% increase in downforce, which provides more grip for braking. And because the flaps are positioned relatively high on the car, the drag on them creates a backward tilting moment, counteracting the forward tilt caused by the deceleration. This greatly improves the balance of the car under braking. All this reduces the braking distance from 150mph to standstill by 10 meters.

Gordon Murray T50 Aerodynamics - Successor to the McLaren F1 supercar

For more information, visit https://www.airshaper.com or email info@airshaper.com
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In this video we explain how to use Paraview to analyze CFD data:

Installing paraview
Visit https://www.paraview.org/download and select the release & operating system that you need.

Loading data
How to load the mesh & field data in Paraview.

Surface Methods
- Surface pressure map
- Surface friction map
- Surface velocity map
- Surface streamlines using SurfaceLIC

Volume Methods
- 2D slices (sections)
- 2D streamlines
- 3D Isosurfaces

State files
Saving & loading your project setup using paraview state files

CFD Results - How to analyse OpenFOAM data with ParaView - 25-minute Tutorial

For more information, visit https://www.airshaper.com
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How to run an AirShaper simulation

Hi, and welcome to AirShaper, the cloud-based simulation platform for external aerodynamics.
In just three easy steps you can obtain all the data & insights you need to understand and improve the aerodynamics of your design.

Fixed wing drone

Step 1 - The Set Up

Start a new project and select the required accuracy. If you’re just exploring initial concepts or simple shapes, a concept simulation will do. If you’re working on the final details or a very complex 3D model, our ultimate simulation is the best choice.

Give the project a name and simply drag & drop your 3D file into AirShaper. By the way, AirShaper is capable of working directly with open surface models. So there is no need to spend weeks to make your 3D model watertight.

On the setup page, first, choose your simulation type. This drone, for example, is above the ground and moving. Fill in the velocity and rotate the model if needed. Finally, let us know the units of your 3D model and if needed, add a scale factor. That’s all there is to it for the setup!

Simply fill in your details on the payment page and submit the simulation.


STEP 2 – The Cloud Simulations

Our automated algorithms will now automatically build a virtual wind tunnel around your 3D model and analyze the aerodynamics. And because it’s a cloud platform, you don’t need any software or hardware and we can use high-performance computing to deliver fast and accurate results.

STEP 3 - The Results

Once the simulation is finished, a full simulation report will be in your mailbox.

You can also view the 3D flow results directly in your browser. Look at pressure, for example, to find sources of drag, analyze streamlines to understand vortex structures and even get insights into which areas are generating wind noise!

And it that is not enough, you can download the full flow results to perform your own post-processing.

For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper


#AirShaper #AerodynamicSimulation #CAD

How to run an Aerodynamic Simulation

For more information, visit https://www.airshaper.com or email info@airshaper.com
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In this video, we explain how to interpret a typical CFD simulation report. The topic is a car and we will learn how to:
- Understand the different forces & moments
- Detect sources of drag
- Read surface pressure & friction maps
- Analyse 3D streamlines
- Interpret sections of velocity & pressure
- Localize sources of wind noise

CFD Results - How to Interpret an Aerodynamic Analysis

For more information, visit https://www.airshaper.com or email info@airshaper.com
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Henrik Fisker has designed the BMW Z8, Aston Martin DB9, Fisker Karma and many more iconic cars. He's now set the target even higher:
to create the World's Most Sustainable Vehicle

History in the Car Design Business
I love designing cars, I would do it even if I didn't get paid for it - I would still be sketching cars in my spare time. It feels like my calling.

Sustainable Vehicles
Over the past 10 years, I've been inspired by people trying to create a better environment and I wanted to do something myself, on a bigger level. So I decided to create sustainable vehicles that are still beautiful, still desirable.

Sustainable vehicles will be there one day, but it will not happen over night - this industry is like an oil tanker that needs 7-10 years to take a dramatic turn. Part of the reason for this is that the lifetime of a new automotive platform, with all the development, crashtesting, investment, ... is about 7 years. Scrapping that after 2 years doesn't make financial sense.

So we'll see dramatic changes over the next 7 years, but even then, we'll need more time to ultimately manufacture truly sustainable cars.

But we cannot sit around and wait, just because they're not perfect yet, and go drive diesel cars again. That's what we are trying to do at Fisker Inc.

Aerodynamics
One key advantage of having an electric car is the flat floor [note: which helps to smoothen the flow underneath the car]. The roof shape was also tuned to help aerodynamics. And the lower front & rear end were also optimized to make sure the air goes around & leaves the vehicle without too much turbulence. Over the years, as a designer, I've learned what things you need to do to optimize this.

But honestly, the goal was not just to design the most aerodynamic car, because then it just ends up looking like most other very aerodynamic cars, which ultimately is a hatchback-style teardrop shape.


Range
The range argument is really only happening right now because we still feel there is a long distance between charging stations and we'll not sure if we'll get there [range anxiety] and have time to fill up the car with electricity.

In my view, over the next 3-4 years, we will see a dramatic increase in charging infrastructure in the US, Europe and China. We'll also get much better at assessing how long we need to stay at a charging station and in the future, we will not necessarily have to wait there for hours. Once people get used to all this, the total range will become irrelevant.


Scale
If all-electric car manufacturers/manufacturers that make electric cars today were using the same battery cell, set of modular electric motors, you would already have scale.

The only way to get scale is to partner up and create some sort of consortium. That is what we are working on and that is how we'll get our price down.

UPDATE:
this interview has also been featured on Clean Fleet Report:
https://cleanfleetreport.com/interview-henrik-fisker-talks-about-the-worlds-most-sustainable-vehicle/

Henrik Fisker Talks -  World's Most Sustainable Vehicle

For more information, visit https://www.airshaper.com
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MV Agusta is one of the teams competing in the MOTO GP - moto2 race class. In this interview, technical director Brian Gillen reveals how they blend physical & virtual wind tunnel testing to improve the aerodynamics of their moto2 race bike.

Wind tunnel testing process
Wind tunnel testing is great: you get a lot of empirical data. But there are a number of steps involved before you get there:
- Test definition: set up the goals & methods of the test plan, which sensors to use, which loads to expect, ...
- CAD design: design the parts for the prototype in a 3D CAD package
- Component prototyping: manufacture the components using 3D printing, carbon fiber, CNC machining, ...
- Mounting on a test bike: mount all the components on a frame (which can be the frame of an existing bike)
- Transportation: move all the required people, equipment and the prototype to the wind tunnel.
- Wind tunnel test: execute the wind tunnel test, monitor the forces, log the data, apply different visualization techniques, set different angles of attack, test at multiple speeds, apply tufts, ...
- Post-processing: process the data into a comprehensive report and draw conclusions

Wind tunnel testing advantages and disadvantages
+ Accurate force & moment data
+ Live feedback
- Indirect visualization
- Challenging to find causality

Wind tunnel simulations
- Traditional CFD programs: the time required to prepare a CAD model (close all gaps & holes) and manually set up a simulation is too long compared to the rapid steps of evolution of the bike in the development process. By the time simulation results were in, they were already 3 steps past with the real prototype.
- AirShaper: take a non-closed model and very quickly put it through the CFD algorithms to get back data. This allowed for very fast iterations to understand where they were in terms of fluid dynamics around the bike.

Data validation
For them, as engineers, data means nothing if it is not validated.
They were able to validate the AirShaper data versus data from the wind tunnel test and found an almost complete convergence in terms of forces & moments on the vehicle.

Virtual iterations
That allowed them to build a virtual avatar around the bike as a mirror image of the physical world. From there on, they could dive into the virtual world for an iterative process before going back to the real world, where testing costs a lot of money. Designing, constructing, testing & scrapping prototypes when they do not work is very expensive.

Track testing
On the track, the drivers can test the real performance of the bike and give qualitative & quantitative feedback to the development team (vibrations at certain speeds, wind buffeting affecting visibility, aerodynamic stability, ...). 
Here too, like in the wind tunnel, you need to be able to correlate numbers to sensation. For this to be possible, the rider has to be very lucid & clear in his description of what he's experiencing on the track (what & where is he experiencing an issue) so that this can be matched to data to find a mathematical reason.

Race Talk with MV Agusta - How to Improve Moto GP Aerodynamics

For more information, visit https://www.airshaper.com
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MV Agusta is one of the teams competing in the MOTO GP - moto2 race class. In this interview, technical director Brian Gillen reveals the top priorities when it comes to race bike/motorbike aerodynamics.

Brian Gillen
Brian is originally from Buffalo, New York, America. He grew up in a family that had a multi-line motorcycle dealership for over 40 years, selling Italian motorcycle brands (Ducatti, MV Agusta, ...), Swedish brands (Husqvarna), German brands (Maico), ...
He's now technical director of the R&D group at MV Agusta: engine design/testing, vehicle design/testing, homologation, styling.

Moto 2
MV Agusta joined the moto2 championship in 2019 with an official team with their technical partner FORWARD RACING (www.forward-racing.com). In 9 months time, they designed a completely new bike from the ground up.

MV Agusta had been following the moto2 series and when the new 3-cylinder engine was introduced, this was a good time for them to get on board: they had been competing with a 3-cylinder racebike in the world championship world supersport. They had a good understanding of what makes a motorbike powered by a 3-cylinder engine perform well.

Aerodynamics
To make the difference within the tightly regulated race class (standard electronics, tires, ...) they looked for areas where they could make a difference and aerodynamics was one of them. Main aspects:
- Coefficient of drag: most want to reduce the coefficient of drag to increase the top speed. But the amount of time you spend over an entire lap at top speed, with wide-open throttle and high rpm, is very limited. Even big gains in top speed advantage result in a limited overall lap time advantage.
- How not to benefit your competitor: on a straight line, people try to get in behind you to go faster by drafting.
- Rider comfort: the engine dissipates a lot of heat and in ambient temperature conditions (like in Thailand) this decreases the mental performance of the rider. Keeping the rider cool is very important to keep his/her mental performance high. A better thermal comfort, relative to the competition, is a strong advantage for the rider.
- Wind buffeting: the air coming off the wind screen can be highly turbulent with frequencies around 20Hz for example which can shake the head of the rider. This reduces the focus, reducing the capability to detect the correct braking point. With just hundreds of seconds to decide on when to brake, this is very crucial.

Race Talk with MV Agusta - Top Aerodynamic Priorities for moto GP bikes

For more information, visit https://www.airshaper.com
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The Italian company Dallara has been building race cars for decades, like the IndyCar IR18, the Formula 3 F3 2019 and the Formula E gen1 and gen2. The founder of Dallara, Giampolo Dallara, has long dreamed of building their own road car and now it's finally there: the Dallara Stradale (Stradale means "road-going"). It has been featured on Top Gear, driven by Chris Harris!

Lowie Vermeersch & Granstudio have once again applied their magic to merge high-performance aerodynamics with pleasing aesthetics. And this video also covers his take on the future of sports cars and their place in our (possibly autonomous) future.

Dallara are super experts in aerodynamics. Still, through the interaction with Granstudio, some aspects of the aerodynamics were changed. The essence of this car is the combination of low weight and aerodynamics. The car creates a lot of vertical pressure, pushing the car against the ground. As it weighs just 800kg, there's not a lot of force wanting to push it out of the corner and thus the relative importance of aerodynamics (and the increase in normal pressure/friction on the tires it provides) makes the car go a lot faster through the corners. The speeds are so high that your mind thinks it's not possible. It creates so much downforce that it could almost drive upside down: the car weighs 850kg and it creates around 820kg of downforce!

But will pure sports cars still be relevant in the future, when we're all driving around in autonomous vehicles? The future that Lowie & Dallara see is the following:

We'll need to move ourselves in much more efficient ways (shared vehicles, ...) to help society. We'll need to take a bit of individuality out of our daily movements.

On the other hand, it's important to leave room for the Homo Ludens, the playful person, to satisfy what Lowie calls "the pleasure principle":
no plan for society will work if it asks us to act according to numbers.

They like to see a future where during the day you move yourself using public transport, shared vehicles and perhaps your own efficient car. And then you go to the track to use (not own) a race car to get that very physical special experience. That's the place they see for a vehicle like the Dallara Stradale in a multi mobility society.

For more information:
www.dallara.it
www.granstudio.com
www.airshaper.com

Lowie Vermeersch talks #4 - The Dallara Stradale

For more information, visit https://www.airshaper.com
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In this 3rd part of our video with Lowie Vermeersch, we're looking at the future of autonomous vehicle design and how aerodynamics will play a role in this!

Lowie Vermeersch questions whether aerodynamics will impact autonomous vehicles or vice versa. The general aspect is that the future needs to move towards higher efficiency to become sustainable and to lower the cost of use.

To provide access to electric cars for many people, the cost still needs to come down. Higher efficiency can further reduce the size & cost of the battery. Aerodynamics is a big part of this efficiency.

This applies to both autonomous & privately owned cars, which will for a long time not look very different. Despite nice concept cars, which are marketing tools to enrich a brands value, actual production cars are always tailored to the human body and physical needs/constraints.

Current car design & layout are determined by drive train layout, fashion, and to a large extent the fundamental functions of a car. That's why a Tesla Model 3 doesn't look too different from other cars. It's largely determined by where the people sit, where they sit compared to the wheels, how you build the cabin around them and so on. So Lowie doesn't see it happening that autonomous cars will look entirely different.

That could happen when we reach totally different laws for autonomous cars (level 5). The visibility you need now is more or less defined by the position of the A-pillar. If you can change that, you can change the design in a more fundamental way and move towards more mono volume shapes.

Vehicle safety is also a big aspect: full active safety will change the structure of a car, which is now strongly determined by passive safety. Lowie Vermeersch did a study at Pininfarina in 2006 forecasting this (the Pininfarina Sintesi Concept Car): the moment that digital systems allow for full active safety (not like the passive safety of today, which is designed to allow cars to crash well) to avoid crashes, then you can get rid of the built-in passive safety.

With fully proven active safety, you can make cars much lighter. This can have a much bigger impact on the layout of the car, as many aspects of the current layout are determined by safety.

Lowie Vermeersch Talks #3 - Autonomous Vehicle Design

For more information, visit https://www.airshaper.com
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Lowie Vermeersch is a famous Belgian Car Designer.
In this second part of the interview, we cover the Lightyear One: the hyper-innovative solar-powered electric car.

Just imagine how difficult it must have been to go from the proportions of a solar-powered prototype racer, all the way to an aesthetically pleasing & technically impressive production car. Here's how they were involved from the first sketches to the final production car.

White sheet of paper
They started with some of the work & research that the team of Lightyear had done. They have a lot of expertise in solar power systems & efficient drive trains. When they started developing the packaging, the proportions, the length/width/height, aerodynamics were really on the plate. An additional requirement was 5m² of solar cell surface. And of course good ergonomics & aesthetics.

Monovolume
Solar race cars typically have a teardrop, monovolume shape. That didn't work for the production, because the visibility lines dictate a huge windshield. This resulted in 3 disadvantages:
- Glass is very heavy
- Less room for solar cells
- Greenhouse effect - the inside of the car heats up. Cooling would require extra energy

Camera's instead of mirrors
The Lightyear One solar-powered car has been fitted with camera's instead of mirrors to further reduce aerodynamic drag. In this case, the camera supports actually improve the aerodynamics.

Covered rear wheel
This was a no-compromise car and covering the rear wheel again helped to reduce the drag. The black stripe around it avoids the visual impression that the car is dragging itself. Together with the strong shoulder, you have an aesthetically pleasing result without compromising aerodynamics.

Wind tunnel testing
The results were record breaking: a drag coefficient Cd of less than 0.20 is the best drag coefficient for a car in this class.

_____________________________________________________________________

AirShaper: www.airshaper.com
Gran Studio: www.granstudio.com
Lightyear: www.lightyear.one
Connect with me on Linkedin: www.linkedin.com/in/wouter-remmerie

Lowie Vermeersch #2 - The Lightyear One Solar Car

For more information, visit https://www.airshaper.com
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Lowie Vermeersch is a famous Belgian Car Designer.
In this first part of the interview, we walk through his career: starting at the TUDelft in Holland all the way to running his own design studio Granstudio in Turin, the heart of the Italian Car Design Industry.

He has the unique skill to design pure, timeless & elegant cars without any form of machoism.
At Pininfarina, he designed the legendary Ferrari 458, an extremely beautiful, legendary sports car. At his own design studio, they worked on a.o. cars like the Dallara Stradale and the Lightyear One solar-powered car.

Lowie likes to talk about aerodynamics: it's an aspect that is often not highlighted when they present their designs, even though it's a very fundamental aspect, for vehicle design as a whole. This links back to his studies at the TUDelft, the Dutch University famous for its expertise in aerodynamics. There, he studied material science, physics, ... which has provided him with a holistic take on car design, which still typifies him as a designer today.

Lowie Vermeersch comes from an artist family (sculptors, painters, ...) and perhaps this has been part of the reason for his desire to have an independent position. He had been fascinated by the independent Italian Car Design studios and went on to do his internship and later work at Pininfarina. A combination of hard work, some merit, some luck, being the right guy at the right moment, allowed him to do great things there. He became responsible for design for the entire studio.

He later founded Gran Studio, where they are capable of working on anything that you can see with the naked eye. They have worked on cars like the Dallara Stradale and the Lightyear One solar-powered car, next to other projects in the broader mobility scene.

_____________________________________________________________________

AirShaper: www.airshaper.com
Gran Studio: www.granstudio.com
Connect with me on Linkedin: www.linkedin.com/in/wouter-remmerie

Lowie Vermeersch #1 -  Ferrari 458 to Lightyear One

For more information, visit https://www.airshaper.com
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In this 4th & final video in the series AIRBUS talks, we continue our discussion on the aerodynamics of the America's Cup and we get insights into their involvement for the 36th edition, where they will support team American Magic.


Simulations instead of physical testing
Due to technical restrictions, it is forbidden to perform wind tunnel or water channel tests. So aerodynamic analysis & optimization is performed through simulations. This can be very costly when the geometry is complex or difficult to mesh, and very powerful high performance computers are required to perform the simulations. And then, many different set points need to be analyzed.


Velocity Performance Prediction
The output of such simulations was used in the Velocity Performance Prediction program: there they can simulate the performance of the boat using the aerodynamic coefficients. That is why they need as many details on the performance of the boat as possible. This approach is very comparable to laptime simulation programs used in Formula One and other racing series.


Interaction between the sails and the boat
One of the problems they found was the detached flow in the interaction between the main sail and the platform of the boat. This detached flow needed to be reduced. The platform acts like a wing tip for the bottom of the main sail, which in theory reduces the wing tip vortex. However, due to the complex flow over the platform and the sail, the wing tip is not so strong and detached flow at the root is a larger problem.


American Magic
Team New Zealand won the previous edition of the America's Cup (35th edition) and it's the winning team that get's to choose the design of the boat for the next edition. They decided to continue with the foils, but changed from a catamaran to monocoque layout of the boat. This is fascinating because this boat design could make the boats pass the magical 50 knots speed barrier. At those speeds, cavitation effects on the foils under water start playing a role.


Strict protocol
Teams are not allowed to inject a gas lighter than air inside the boat to lift the boat from the water. All the crew should also be human (no robots yet!)

AIRBUS talks part 4 of 4 - America's Cup Aerodynamics - PART 2

For more information, visit https://www.airshaper.com
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In this third video in our series AIRBUS talks, we take a look at the aerodynamics of the America’s Cup boats.

History of the America’s Cup
The America’s Cup is the oldest sports competition in the world. The original race was between British & American ships, sailing around the Isle of Wight. The technology level is on par with Formula 1 and budgets are equally high.
In the last 3 America’s Cup, the contenders have used the foils to carry & lift the boat out of the water. Once the boat is lifted from the sea, it wins a lot of speed and aerodynamics become more important. Not just for the sails, but also for the entire platform:
- Detached flow from the crew
- Flow over cavities
AIRBUS can inject their expertise in these domains.

New challenges
With the hull coming out of the water, it becomes a relevant & active aerodynamic part. The biggest challenges AIRBUS had been to reduce the drag of the trampoline (which the crew uses to cross sides). Another challenge was to compare the drag of different hull shapes and crew positions.
Also, the interaction between components is very relevant. The front & rear beam connecting the left & right hull play a large role for the aerodynamics. They even apply vortex generators to reduce the drag!

Stay tuned for the fourth and last video, where we'll discuss the upcoming 36th edition of the America’s Cup!

AIRBUS talks part 3 of 4  - America's Cup Aerodynamics

For more information, visit https://www.airshaper.com
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Air Race E is like nascar racing in the sky:
Electric planes racing at speeds of 300MPH around an oval track just 10 meters above the ground!

In this interview with Izan of Air Race E, we discuss how electric plane design is changing air racing and aviation as a whole:

Concept
Air Race E is a new class of motorsport based on electric aircraft. The format is similar to Nascar, with 8 airplanes racing in an oval circuit 10 meters above the ground. High-speed intense motorsport.

Airplane Design
- The front end of the aircraft
The electric powertrain is a lot more compact and this allows for a more compact nose cone. Also, no air intakes are present, making it more streamlined.
- Propeller layout
Regulations will be opened up from single-axis propellers to distributed electric propulsion. This is a hot topic in the urban mobility movement with companies like Joby Aviation, Uber Air, Lilium, CityAIRBUS and many others.
Distributed power along the wing becomes possible. Or putting the rotors at the wingtips to counteract the wingtip vortices & increase efficiency.
- Battery distribution
These can be located in the wing, tail, nose, ... the distributed weight allows for new architectures as well.
- Part count
There is a large reduction in part count & operational cost per flight hour compared to traditional fossil fuel

Nascar in the Sky - Interview with Air Race E

For more information, visit https://www.airshaper.com
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In this second video in our series 'AIRBUS talks' we dive into the different methods that are used to design a modern airplane:
- CFD (computational fluid dynamics): aerodynamic simulations running on high-performance computers
- Wind tunnel testing: using scaled models inside a wind tunnel to analyze multiple set points
- Flight testing: flying the real airplane to map its behaviour, performing reject take-off scenario's, stall angle detection, ...

AIRBUS gives us insights into the benefits of these methods:
- CFD: it's possible to simulate the real Reynolds number - the real speed & size of the airplane
- Wind tunnel testing: you can analyze multiple setpoints over a single campaign
- Flight testing: the one & only end evaluation

Most of the efforts are focused on cruise flight, as this represents 90% of the operating regime of the plane.

We also zoom in on the challenges of keeping the Reynolds number the same. AIRBUS even goes as far as working with different gases at low temperature & pressure to get the same Reynolds number as the real aircraft! They've performed tests at DNW (German-Dutch Wind tunnels), ETW (European Transonic Wind Tunnel), DLR (Deutsche Luft & Raumfahrt) and more.

Coming up next:
How AIRBUS was and is involved in the America's Cup!


For more information, visit:
www.airshaper.com
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#AirShaper #AircraftDesignTools #AirbusAerodynamics

AIRBUS Talks - Aircraft Design Tools

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'AIRBUS TALKS' is a series of 4 videos with Julián Maldonado: he explains the ins & outs of aviation design and the America's Cup boats they help design.

Part 1: Aviation Challenges

In this first video, Julian explains the modern challenges in aviation and how they plan to tackle these.

About Julian Maldonado:
- Has been working at AIRBUS for 15 years
- 10 years on aerodynamics: CFD, wind tunnel testing, flight testing
- 2 years on flight dynamics: A320neo, flight test identification
- 3 years on aircraft performance: project manager

Typical general aviation challenges - related to the aerodynamics:
- Safety first
- Reduce emissions: CO2, NOx, Noise

Aerodynamic focus points:
- Laminar flow: reducing turbulence & drag
- Improving the lift/drag ratio: improve performance & optimize the trajectory

Improving the overall drag of the airplane:
- Winglets: 2% drag reduction. Applied to every flight, this has a huge impact.
- Laminar flow: the BLADE project focuses on improving laminarity on the wings to reduce the drag.

Coming up next:
Simulation techniques, wind tunnel testing & flight testing


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#AirShaper #AviationChallenges #AirbusAerodynamics

AIRBUS Talks - Part 1/4 - Aviation Challenges

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In this video, we’re analyzing how aerodynamics impact the performance of rally cars.

Surprisingly enough, in many ways the aerodynamics of rally cars are far more complex than in Formula One, where the cars enjoy some of the world’s smoothest and grippiest bits of tarmac. That’s quite a big contrast to rally cars, where driving in a straight line without wheel spin, drifting or jumping is a rare occasion.
So, where do you start if you want to optimize the aerodynamic performance? The hard reality is that you’ll have to look at multiple scenario's and strike a delicate balance between aerodynamic performance in each of those.

Let's take this 2016 Skoda Rally car in normal setup (regular ride height) and straight-line driving at 40 m/s as the reference. As shown by these red clouds, which indicate where a drag-increasing wake is created, this clearly isn’t the most streamlined car out there:

The rooftop air intake disturbs the air to such an extent that in its wake the center of the rear wing loses pressure and performance. And those wheel arches cause a lot of separation of the airflow at the sides of the car.

But enough on theoretical straight-line driving – it almost never happens, it’s time to start jumping & drifting!

If we increase the car's ride height by 15cm, which is not uncommon just before or during a jump, then the drag on the car increases by 16% and the downforce is cut in half! As you can imagine, losing downforce and grip just before take-off can be quite tricky for the launch. And once you’re flying, you’re slowing down quite a lot because of the drag!

Massive changes in ride height like this are one of the main reasons it’s difficult to boost rally car performance by using underfloor aerodynamics, diffusers and so on: the downforce they generate is extremely sensitive to changes in ride height. And perhaps even more important, that change of downforce can be more pronounced at the front or the rear, changing the aerodynamic balance and thus the handling & stability of the car.

Next, let's look at drifting. Obviously, there's enough debate going on already as to whether you'll be faster or not when drifting. When it comes to aerodynamics, the drag on this car increased by 43% at a moderate drift angle of 15°! That would slow you down quite a lot. But there's good news as well:

The entire car starts acting like a giant wind shield, with the wind hitting the outer side flank. This generates around 100kg of lateral force pushing the car back into the corner.

And, interestingly, the wake of the rooftop air intake is no longer affecting the rear wing, which is now happily creating downforce, so it seems that this car really comes together in the corners.



Note: the 3D model of the rally car used in this video was a public one from hum3D.com and is not an official model from Skoda: it serves mainly to highlight general rally car challenges and not to make official claims to the performance of this car in question.


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#AirShaper #RallyCarAerodynamics #SideSlip

Rally Car Aerodynamics - Side Slipping through the Air

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In this video, we’ll cover the advanced aerodynamic features of the upcoming Lotus Evija electric hypercar.

From a distance, the Lotus looks relatively normal, at least for a hypercar. But the closer you get, the more hidden channels you discover. At the front, underneath the hood, the air is guided between the wheels and the center of the car, to exit a bit further downstream at the sides of the car. The air that has chosen to go on top of the hood, tumbles down to the flanks to enter the air intakes on the side of the car to exit at the back.

We didn’t yet obtain a 3D model of the Evija, but we have something that comes quite close. The Aquilo is a concept car I designed 10 years ago, featuring roughly the same channels. Let’s have a look at how they help to improve aerodynamic performance.

In this concept, the air enters the car in the middle and then splits left & right to exit on the sides. This helps to reduce the virtual frontal area of the car, something Lotus refers to as aerodynamic porosity. This same porosity can be seen at the back, where large channels take the air in on the sides and spit it back out at the rear. This air helps to fill the low-pressure bubble at the back of the car, greatly reducing the wake it leaves behind, as shown by these red pressure clouds. This helps a great deal to reduce the drag of the car and thus increases range and top speed.

Beyond reducing drag, the channels in the Aquilo are meant to split the air left & right in an asymmetric way. This generates lateral forces to help the car corner faster. The concept was patented and later on referenced to in patents of Ferrari and Toyota. So perhaps the Lotus Evija hasn’t revealed it’s full potential yet, let’s see what the future brings!


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#AirShaper #HypercarAerodynamics #LotusEvija

Hypercar Aerodynamics - 2000hp Lotus Evija

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In this video, we’ll discuss the motorbike aerodynamics with together with Joseph Katz, author of the famous book “race car aerodynamics”, professor at the San Diego State University and passionate motorbike rider.
Before we move on to the interview, let’s summarize some basic aspects of motorbike aerodynamics and how they differ from cars:

First of all, the drag: the frontal area, which is the area when looking at an object from the front, is much smaller for a motorbike. But to get the total drag on an object, you need to multiply this frontal area by the drag coefficient, which is much, much larger for a motorbike, offsetting the benefit of the smaller frontal area: it is filled with exposed bits of geometry like the wheels, brakes, and so on, and the surface the air needs to follow is hardly a smooth one: it’s full of abrupt changes like the end of the wind shield causing the flow to detach. And then there’s the rider, a massive disturbance to the air. So, the drag coefficient of a motorbike is easily double or more than that of a modern-day car.
Second of all, the centre of pressure, which is the point where the total sum of the pressure is acting, is quite high above the ground. With respect to the contact point of the rear wheel on the ground, this tends to push the motorbike backwards, lowering contact pressure on the front wheel, which reduces steering control. As the aerodynamic drag force increases with the square of velocity, this can become problematic at high speeds. So, trying to get the center of pressure as low as possible is crucial for motorbikes. A low rider position is a good start. Another way to balance things is to create down force on the front wheel to counteract this back-flipping moment on the bike.

In the interview, we cover the following topics:
- Effects of leaning on aerodynamics
- Engine performance
- AMA superbikes
- Rider position
- Rear tire wear
- Active aerodynamics
- Wind tunnel testing
- Centre of pressure
- Ducati wings
- Lateral forces
- Helmet vibration
- Better engine performance via RAM air


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#AirShaper #MotorbikeAerodynamics #SportsAerodynamics #JosephKatz

Motorbike Aerodynamics - 10 mph faster with Joseph Katz

Open wheels, exposed components and a constantly moving rider makes optimising motorcycle aerodynamics a huge challenge. But there are many techniques engineers use to refine the designs of motorbikes, helmets and suits and the rider has an important role to play too.

How to improve Motorcycle aerodynamics

For more information, visit https://www.airshaper.com
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In this video we’ll explain how you can build aero maps for your own race car.

What are aero maps?
So, what exactly is an aero map, and what on earth do maps have to do with race cars?
Well, in general terms, a map is a tool to visualize or store the relationship between different variables. Like the altitude of a terrain in function of longitude and latitude. Or, in case of a race car, the aerodynamic drag, lift and balance in function of the setup of the car, like the ride height at the front and the rear, the angle of a wing, and so on. So in general, aero mapping can be described as the “mapping” of the relationship between geometric parameters of the car on one hand, and the effect on aerodynamic properties on the other hand.

What do you use them for?
So why do you need an aero map? When the time has come to race, every second matters: not only for lap times, but also for setting up the car prior to and during the race. Aerodynamics are crucial for the dynamic behavior & performance of the car. For example, the aero balance describes how the down force is distributed between the front and rear axle. Shifting this balance can help mitigate oversteer for example. Another aspect is the cornering performance: when the circuit is filled with high-speed corners, you need more down force. But on circuits with long straights, the drag penalty associated with high-down force settings will slow you down over the course of a lap. Having a clearly mapped relationship available between the setup parameters of the car and the aerodynamics is essential to setup or modify the car on race day – when there is no room for trial & error.

Where can you get these aero maps?
“Ok, you have me convinced, I need aero maps. Where do I buy one?” Unfortunately, it’s not that easy, for a number of reasons:
a. You could ask the manufacturer, but quite often the aero maps are not shared, or the ones that are shared are not always accurate or useful.
b. You could also consider building your own aero maps in a wind tunnel: it can result in highly accurate maps, but requires large budgets as a proper tunnel with moving floor costs thousands of euros per hour, not even taking the cost of preparation & data processing into account.
An interesting budget-friendly way of building aero maps is to run CFD, or computational fluid dynamics simulations on the different setups of your car. Let’s have a look at how this can be done.


Building an aero map through simulations
First of all, you’ll need a 3D model. Again, it’ll be tough to get it from the manufacturer, but luckily, there’s plenty of professional modelers out there that provide high-quality 3D models of race cars for just a few hundred euros. And with AirShaper able to run simulations directly on such models, which can contain many gaps and holes that normally crash simulation, you can use these models as they are, or have us modify them to match your car in specific.
To illustrate the process of aero mapping we’ll be using this public 3D model of the 2016 Audi R8 LMS. We changed the ride height of this car by 20mm in two steps and then mapped two important aerodynamic properties.
First, the drag and down force. As you can see, increasing the ride height of the car doesn’t impact the aerodynamic drag much but it significantly reduces the down force. This is because you reduce the speed up of the air underneath the car, helped by the splitter at the front and the diffuser at the back. So lowering the car would actually be a better idea in terms of aerodynamics, giving you extra down force at hardly any drag penalty, so why didn’t we?
Well, in most race classes there is a lower limit to the ride height of the car, so you wouldn’t be allowed. And, if you lower the car too much, you can actually block or choke the flow underneath the car, losing that precious down force.
But down force is more complicated than just a single number. As mentioned before, the aero balance describes the distribution of down force between the front and rear axle. Too much on the front will make the front wheels grip nicely but allows the back to lose grip easily, resulting in oversteer. So, it’s important to tweak the balance properly and amongst many things, align it with the weight distribution of the car itself. In this example, we can see that increasing the ride height of the car, also shifts the aerodynamic balance backwards. To counter this, you may need to play with the front splitter or the angle of attack of the rear wing, or the rake of the car, if allowed by regulations.


For more information, visit:
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#AirShaper #CarAerodynamics #AeroMap

Race car aerodynamics #3 - Aero mapping

Aero maps visualise the relationship between downforce, drag and ride height. Engineers use aero maps to tune the set-up of a race car to achieve maximum downforce and optimum aero balance in the corners where the most lap time can be found.

How aero maps can improve race car performance

For more information, visit https://www.airshaper.com
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Tesla Semi Explained: https://www.youtube.com/watch?v=Km1NHe0ZsVo

---What is Vecto---
Within the quest to limit climate change, the pressure on heavy duty transport has been rising, and with good reason: trucks, buses and coaches together produce around a quarter of all CO2 emissions from road transport in the European Union. To ensure that the most fuel-efficient vehicle combinations are brought onto the market, the European Union developed the “Vehicle Energy Consumption calculation Tool”, or VECTO in short, a mandatory tool since January 2019 for new trucks & buses in a number of categories. Based on input parameters like rolling resistance, air drag, masses and inertias, gearbox friction, auxiliary power and engine performance, it simulates fuel consumption and CO2 emissions based on standardised driving cycles. So how do you obtain all these parameters?


---What is Vecto AirDrag---
Based on constant speed track tests and a massive set of measurement data, Vecto AirDrag allows you to calculate the air drag Cd*A, based based on force measurements:
- Constant forces, that do not change with velocity (rolling resistance, bearing losses, and so on)
- Air drag force, which scales with the square of the velocity
To obtain the split between these forces, you can measure the force at 2 different velocities. If you then fit a curve through both low-speed and high-speed tests, including a constant and a quadratic term, you can isolate both components.
***The Track***
Tests are executed on a proving ground test track, with two straight parts running in opposite direction. Data is logged throughout the entire test, but it’s only the data captured on these straights that counts.
 
***Measurements***
- On the vehicle
High-accuracy DGPS data
Front axle rpm & torque (left and right)
Wind speed & direction above the truck measured using an anemometer mounted on a pole
Ambient temperature on the truck
- At the fixed weather station on the proving ground
Ground temperature and
Air pressure & humidity are measured.

 
***Data evaluation***
Once all the tests have been performed and the data has been gathered, the constant speed tests are processed in 8 steps:
1: the instantaneous velocity readings are corrected using the average velocity over a test section.
2: the forces acting on the truck are calculated, based on the torque readings from the shafts and the engine or cardan speed. These are then corrected:
- the force for climbing or descending is compensated for based on the road gradient & vehicle mass.
- the correct air density is calculated using the temperature at the vehicle and pressure & humidity at the fixed weather station
3: validity criteria are applied to each constant speed test (speed & temperature ranges, ...)
4: CdA(beta) is calculated for each test by fitting a curve through the data.
5: result averaging per heading and then across headings.
6: extra checks (on rolling resistance, ...).
7: CdA(beta) conversion to CdA(0°) based on empirical data / vehicle type.
8: anemometer drag correction

---Optimizing for efficiency--
As you can imagine, running these tests requires large budgets & a lot of preparation effort, so you want to get it right the first time around. To know up front how changes in aerodynamics will impact vehicle efficiency, you can run aerodynamic simulations: 12--these allow you to calculate the CdA for each design concept and quantify the effects of replacing mirrors by camera’s, shielding the wheels, reducing the gap between tractor and trailer, and so on.
You can then use the engineering mode of Vecto to assess the effect of these differences in aerodynamic coefficient on total vehicle efficiency. Once you’re comfortable enough with the predicted efficiency gains, you can move on to real physical testing, using the declaration mode of Vecto for the final analysis.

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#AirShaper #VECTO #ReducingCO2emissions

Cutting truck & bus emissions - The Vecto AirDrag Tool

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In this video, we’ll guide you on how to select the right simulation for your project.

In theory, the advice is simple: go for the one with the highest resolution, as it results in the highest accuracy & the most useful data. But in practice, this is also the most expensive & time-consuming solution, so the real question is:
“Within a given budget & timeframe, how can I improve the aerodynamics the most?”

For example, should I run 10 simulations at low resolution or one at high resolution? The answer is to select the right resolution for the right purpose. 

But first, let’s explain what exactly resolution means for aerodynamic simulations:
Very similar to the pixels of a digital photograph, which form a 2D grid or mesh, a flow simulation uses a 3D mesh, featuring small blocks around your 3D model to calculate the aerodynamics. For more details on this, watch our separate video on computational fluid dynamics using the link in the description below or at the end of this video. Most important aspect: the higher the resolution, the smaller these 3D blocks become and the more accurate the flow simulation will be. That brings us to the first guideline on how to select the right resolution, the 3D model you’re analyzing.

3D model
Let’s compare the effect of low, medium and high resolution on the same object, in this case, a Formula E car. At low resolution, the global mesh looks quite ok but in areas, with small details like the wheels the mesh is quite rough. Depending on how accurately you want to capture the flow around these details, the mesh resolution needs to increase accordingly.
So if you’re interested in the global flow around a smooth object, a low resolution might be enough for a first idea. But if you’re interested in the flow around small details on a large 3D model, you may want to go for a high resolution.

Accuracy
Next up is the accuracy. Your shape may be simple, like an airfoil, but to accurately analyze lift & drag forces, you still need a high resolution. So if you’re simply interested in learning about the order of magnitude of forces, like the difference between 1 or 10 Newtons of lift, a low resolution might do. But if you’re looking to make more accurate force estimations, to know whether the lift on your airfoil is 6 or 6.5 Newtons, you’ll need a high resolution.

Design phase
Finally, it also depends on the design phase of your project. If you’re in the very initial phase, you first want to gain basic insights and not spend all your budget on simulations just yet. So a low resolution might be enough to provide you with those first valuable learnings and relative ranking between concepts. But as you progress towards more detailed models with smaller differences, the resolution needs to evolve accordingly.

This means you could for example run 10 simulations at low resolution to determine the main design direction during the concept phase, run 5 simulations at medium resolution when you’re detailing a selected number of designs and finish off with 3 simulations at high resolution to tweak the last bits of performance before releasing the design for physical wind tunnel testing or production. 

So in conclusion, a low resolution might be enough if you’re working on simple, early-stage 3D models and just need a ball-park estimate on the forces and the flow field. But if you’re looking to make accurate force predictions on complex 3D model towards the end of your design process, you’re better off with a high resolution.

Last but not least: talk about it. If you’re not sure how to approach things, just get in touch and we’ll see how we can help!

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this in the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it?

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#AirShaper #SimulationSuccess #SimulationProjects

Choosing your Simulation - Accuracy vs Speed vs Cost

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In this video, we’ll explain the basic principles of CFD or computational fluid dynamics.

Let’s start with computational: this means that in contrast to physical flows, CFD flows are simulated using computers. For simple problems, this can be done on your laptop. For bigger problems, in automotive or aviation, for example, huge clusters with thousands of cores and terabytes of memory are often used.

Secondly, it involves a fluid, which can be a liquid or a gas. When you’re working with water, it’s called hydrodynamics. When you’re working with air, it’s called aerodynamics.

Last but not least, it involves dynamics, which relates to the fluid movement.

So how does one compute a flow? 

Modeling involves the continuous mathematical functions that you use to describe the real flow. In reality, that flow is the result of many different laws of physics working together. To limit computational effort, it’s a matter of selecting only the ones that have a substantial impact on your flow topic: if you’re calculating the aerodynamic force on a wing, for example, there’s little use in taking the gravitational pull of the moon into account, as the effect is negligible. So, defining correct & relevant models is important to limit the modeling errors:

In case of fluid mechanics, the most important model is a set of partial differential equations called the “Navier Stokes” equations. These basically apply the laws of Newton for every small bit of the fluid, stating the dynamic balance between the forces acting on it and the change in its momentum. This conservation of momentum, together with the conservation of mass, allows you to describe the flow field.

For some very simple cases, like laminar flow through a pipe, there are analytical solutions: the entire flow field can be described using continuous mathematical functions. These allow you to calculate the exact velocity & pressure for any given location in the flow field at an infinite resolution.

But for anything more complex than these very simple cases, we don’t have such an analytical solution. That means we need to break down reality into small blocks for which we do have a solution. These blocks can be finite elements or finite volumes, also called cells. Think of it as the difference between analog and digital photography, where a complex image is described by simple pixels, each having just one color.

This process of breaking down a large continuous flow field into small cells is called meshing. For each of these cells, we can approximate the continuous Navier-Stokes equations by discrete algebraic equations. These allow us to calculate the pressure & velocity at the center of each cell, which is called the node, based on the values of velocity & pressure of the surrounding nodes.

The higher the order of these discrete approximations, the more surrounding nodes are included. This “reach” is called the computational molecule, resulting in a set of algebraic equations for each node. As the value of one node depends on the value of neighboring nodes and vice versa, the equations are connected. This means you need to solve them simultaneously by putting them together in a big matrix.

But before we discuss how to solve this matrix, we need to talk about the discretization error: “The difference between the exact solution of the governing equations and the exact solution of the discrete approximation”. The more cells you apply, the smaller this error. But this also increases the number of equations you need to solve, and with meshes typically containing millions of cells, this quickly becomes very expensive. So you’re best off applying small cells to locations where the flow is complex, and large cells where the flow is less curvy, typically further away from the object.

Once you have defined your mesh and your matrix of equations, it’s time to solve them. It’s possible to find the exact solution of this matrix problem through a direct method like Gauss elimination or LU decomposition. But this is very costly in terms of computational power and why bother solving the equations down to computer accuracy level, when your discretization error is much bigger anyway?

This is where faster iterative methods come in: they start by “guessing” an initial solution, which could even just be a standstill flow field, or “zero velocity” for every point. Then they linearize the equations around that point and improve the solution through iteration. If you iterate long enough, the flow field will converge to a stable solution, reducing the iteration error. The difference between this solution and the direct solution of the equations is called the iteration error.


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Computational Fluid Dynamics Explained

Computational Fluid Dynamics is used in many industries to model and optimise the behaviour of fluids. Based on the Navier Stokes equations, there are three steps to computing flow, modelling, discretisation and linearisation.

Computational Fluid Dynamics (CFD) explained

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Aerodynamic backpack ventilation – Vaude has your back

Why do we sweat when we exercise?
Well, we like to keep our body temperature constant and when doing sports, that temperature increases. To counter that, we sweat. The sweat evaporates into the air around your body and the energy needed to do so is drawn from your body, cooling it down.

But what if you’re blocking the air? Then the sweat piles up and you’ll need to sweat even more in other places to get enough cooling. It leaves commuters with a soaked T-shirt on the back and athletes with decreased performance.

So Vaude turned up the technology level on their newest backpack to come up with a solution for this. In a first step, they ran several airflow simulations on a digital mountain biker without a backpack, simply to understand how the air moves around the body and find sources of cooling. They saw that the airflow around neck & shoulders re-joins at the higher part of the back, to then channel down at relatively high speed before letting go somewhere lower down the back.

At some point, the air going around the torso was also considered to help drive air underneath the backpack. But with the air being too turbulent after going around the torso and the backpack hidden in the wake of the rider’s back, this turned out to be less efficient.

So together, we figured it would be quite nice to use the central airstream at neck & shoulders to help cool down the rider’s back in the locations where it matters most: the central part of the lower back. Multiple concepts were thought of, all with the aim to capture this airstream and channel it between the rider’s back, and the backpack itself.

Aerodynamically optimized channels were carved out of the padding between rider and backpack and after numerous checks via simulation, we ended up with a design that outperforms anything that is currently out there in the market.

And that’s not just us talking: Vaude performed multiple wind tunnel tests, with riders going at it in well-controlled conditions, like the temperature, seating position, produced power and so on. They even went to the Sports Tech Research Centre, who operate a specialized wind tunnel, to put their new backpack design to the test.

-----------------------------------------------------------------------------------------------------------

Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it?

For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #BackpackVentilation #SportsAerodynamics #Vaude

Sports Aerodynamics #3 - Aerodynamic backpack ventilation

For more information, visit https://www.airshaper.com
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Sadly, it’s true: solar panels can really fly and about a decade ago, reports of damage to and by solar panel systems were a common thing after a storm. So what happened? 

On a small scale, you can mount perhaps 20 solar panels flush to the angled roof of your own house. On a large scale, there are vast arrays of thousands and thousands of solar panels installed on the flat or nearly flat roofs of industrial buildings.

Let’s focus on these flat roof systems. 
Penetrating the waterproof coverage for anchoring purposes isn’t always an option, many operators just put ballast of weight on the mounting system to keep things down. That avoids a possible leakage problem but adds a new one: extra weight. 

A decade ago, when no norms were available yet to determine the right amount of ballast to keep the panels down, some applied more safety than others. And with the financial crisis in full force back then, there was yet another incentive to get the total weight below the capacity limit of the roof to get projects approved and profitable. So sadly, some panels flew away.

Nowadays though, through extensive wind tunnel testing & simulations, norms have been formed and it’s clear & simple: follow the norm. Still, those norms allow for optimization, as they often take the aerodynamic behavior of the system into account. So prior to final wind tunnel testing & certification of a system, it makes a lot of sense to integrate aerodynamic simulations into the R&D phase to optimize the mounting systems.

To illustrate this, we’ve analyzed a single free-standing panel in an airflow of 40 m/s, a pretty decent storm. Under headwind, the vertical lift on the panel is around 240 kg, so the weight of the panel itself, around 20kg, is not nearly enough to keep it down.

This happens because the panel behaves like a wing with ground effect: the air hits the bottom of the panel, creating a high pressure pushing it upwards. At the top, the air separates as it jumps over the panel, creating a large suction effect again pulling the panel upwards. Even when the wind hits the panel under a large angle, the lift force can still be as high as 100kg.

If we look at the same panel receiving headwind, but now surrounded by neighbors in an array, the vertical lift force increases even further. Why? The free-standing panel had an escape route for the air on both sides. But when flanked by two neighboring panels, the only way for the air is up, increasing the pressure build up. The panels on the second, third and fourth-row feature much lower lift values, and sometimes even downforce. That is why very often the ballast for the outer panels of the array is much higher than the ballast for the inner ones.

Now if we rotate the entire array by 45°, we see some other interesting effects. As expected, the panel at the corner feels the highest vertical pull, but it’s lower than the headwind case. As we move away from the corner, the lift on the front row panels decreases significantly. Nevertheless, values are still very high and too much ballast would be needed to keep them down. So to reduce wind loading, plates are usually installed to prevent the air from entering underneath the panel, which reduces the high pressure build up at the bottom side.

We’ve added such a plate to the isolated panel. The air now hits this backplate, pushing the plate itself downwards as the air jumps up. The lift on the total system has been reduced drastically for all angles and even features downforce at some angles. The solar panel itself, however, can still feel the suction effect in the wake of the plate.

To counter that, there are some innovative systems that feature an intended opening at the top of the backplate. The suction effect, which is the largest just at the top of the backplate, will now draw air from underneath the panel. This helps to both reduce the pressure below the panel and to reduce the suction effect at the top. The effect on the vertical forces is quite clear!

Studying the behavior of a system in clean airflow is just the beginning though. In real life, complex wind flow patterns around the building itself, influenced by the surrounding terrain and featuring wind guests, add multiple layers of complexity to the problem. So complementing simulations with wind tunnel testing and adding the right safety factors is key to keep your panels from flying.

Wind tunnel image courtesy of Peutz

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

Renewable Energy - Solar Panels Can... Fly?

For more information, visit https://www.airshaper.com
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In this video, we’ll be playing with the aerodynamics of the Porsche GT4 race car.

Some people are satisfied with buying a standard Porsche GT4 to go racing. And to be honest, I’d be quite ok with that as well, if I had the budget. But others get creative and start modifying their car to gain that extra bit of performance.

Volker Wawer is one of those people: he wanted to fit wider tires on his GT4 and that meant he needed to shield those tires using wider fenders. But these impact the airflow around the car, possibly blocking the air going into the side air intakes further downstream. As reduced pressure & airflow rate at the inlets translates into a loss of power, Volker wanted to check this using aerodynamic simulations.

There was one problem though: getting a 3D model from Porsche is not so trivial. As an alternative, there are near-exact 3D models made by skilled 3D drafters, which are available for purchase online. As these models are built for visualization purposes, they’re usually built using surfaces and feature quite a lot of gaps & holes. This causes aerodynamic software packages to crash, so we put a lot of effort into it at AirShaper to make our algorithms able to work directly with these so-called open surface models.

So we purchased a Porsche GT4 model and had the wider fenders modeled onto it. We launched 2 Detailed Simulations: the normal GT4 and the one with modified fenders, to clearly see the difference. And we found some interesting results.

To understand how the air flows around the side of the car, we released particles just upstream of the car’s front left fender and traced their path. This showed us that the air that eventually ends up at the side air intakes, doesn’t just come from air going around the side of the car. Part of the breathing air for the engine first rises on top of the front hood of the car, to then tumble down to the side flank of the car after the front wheel arch.

Interestingly, the new front fenders are able to sustain this high airflow on the front hood over a longer distance, reducing the amount of air that passes via the sides, where it loses momentum and gains turbulence at it passes over the front wheels. We measured the pressure at the air intakes for both cars and actually found a higher pressure for the car with the modified fenders.

It doesn’t happen too often, but in this case, Volker got both the wider fenders and a power boost for the engine. In racing, it’s impossible to fully isolate driver & car performance, but both must have been pretty good as he won his next race at the Nürbürgring.
That was it for this video on Porsche GT4 aerodynamics, thanks for watching and see you soon!

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

For more information, visit:
www.airshaper.com/race-car-aerodynamics
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#RaceCarAerodynamics #AirShaper #PorscheGT4

Race Car Aerodynamics #2 - Improving the Porsche GT4

For more information, visit https://www.airshaper.com
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In this video, we’ll show you how aerodynamics can impact the performance, safety & environmental impact of your design!

Let’s start with aviation.
The most obvious field in aerodynamics.
Now the pinnacle of airplane performance is the Red Bull Air Race. Apart from big engines and big balls, aerodynamics determine who wins and who loses. Australian team Matt Hall Racing used AirShaper to optimize the airflow around key components of their plane. They won several races that season and nearly took the overall win!

Drones are another hot aviation topic 
Getting the aerodynamics right is crucial to fly as long and as far as possible on a single battery charge. For their latest model, the eBee X, senseFly ran several AirShaper simulations to optimize the vortex, or the corkscrew motion, of the air at the tip of the wings. By tweaking the vertical winglets together, we increased the aerodynamic efficiency by 30%! 

Aerodynamics also play a key role in performance sports, like cycling or skiing. We used a 3D scan of a speed skier to improve the aerodynamics of his stance & equipment. We helped him take his personal record from 198 km/h to a whopping 214km/h! At those speeds, aerodynamic forces dominate anything else!

But what about safety? 
Let’s have a look at the Sunfold, a free-standing container equipped with solar panels at the top to capture and store energy! Tiger Power uploaded a 3D model of their entire system into AirShaper and analyzed the forces and the moments caused by the wind to see if would tip over. 

Luckily, it didn’t!

The next step is to put all that renewable energy to good use, like efficient road transport. We benchmarked the Tesla Semi versus an optimistic generic truck and found a reduction in aerodynamic drag of around 20%! That’s over 5.000$ of fuel savings each year for a conventional truck, not to mention the reduction in emissions!

So whether you’re cycling at 30 km/h, transporting cargo at a 100 km/h or racing at 300 km/h, aerodynamics matter big time.

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #Aerodynamics  #Aviation

Why aerodynamics matter! - Performance, Safety, Environment

For more information, visit https://www.airshaper.com
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In this video, we will analyze the aerodynamic features of the Tesla Semi truck.

Emissions
First, some context. Lately, heavy-duty transport has been facing increasing pressure: in Europe, trucks, buses, and coaches together produce around a quarter of all road transport CO2 emissions.

On the power consumption side, efforts are made to reduce aerodynamic drag, as it is responsible for more than half of the power required to drive a truck at highway speeds.
Truck aerodynamics

But improving truck aerodynamics is not easy: typically, trucks and trailers are bulky objects that have been stretched to make use of every cubic centimeter that is allowed by road regulations, such as maximum length, height & width. It’s not hard to see that trucks are not exactly super streamlined, but exactly how bad is it?

Aerodynamic efficiency is expressed via the drag coefficient Cd. If you want to learn more about the drag coefficient, just watch our separate movie on this. In short, lower is better with the Tesla model 3 at 0.23 and a conventional truck between 0.5 to 1. So when Tesla claimed 0.36 for their Tesla Semi truck, we jumped up and wanted to know more.

3D model
We called Elon Musk and asked him to send us a 3D model of the truck within 2 weeks. But he’s not too good with deadlines and we didn’t want to wait, so we asked our partner engineering agency Voxdale to build a 3D model for us instead.

Results
And believe it or not, we got a drag coefficient of 0.35 for the Tesla Semi truck! You can argue that we didn’t use the exact geometry for example, but even compared to our optimistic conventional truck it featured a 20% drop in aerodynamic resistance! That’s over 10% reduction in fuel consumption or 5000 liters of fuel per year!

Let’s start at the front: the vertical frontal face of the boxy conventional truck causes a huge pressure build-up on this entire surface, as the air needs to take a 90° turn to get around the cabin, either over the top or around the sides.
To provide smoother escape routes for the air, the Tesla Semi’s cabin features a strong backward inclination angle and large smooth corners around the sides of the cabin. This allows for a much more gradual evacuation of incoming air and thus a lower pressure buildup.

On road cars, the mirrors make up 2 to 5 % of total drag. On trucks, they are much bigger and Tesla decided to simply replace them with tiny camera’s mounted on aerodynamic wing-shaped beams! It’s quite easy to spot this difference by looking at the wake caused by both mirror setups!

If the roof spoiler is too wide or too high, this can leave a large wake and create unnecessary drag, as we can see at the top of our conventional truck. If it’s too low or narrow, the air will hit the square front of the trailer, causing local pressure to build up and separation downstream. Tesla made sure the Semi cabin fits nicely with its trailer: they were able to do so by extending the side spoilers all the way to the trailer and by leaving just enough space in top view for the trailer to rotate.

The wheels. Covering the front wheels is quite difficult, as they need room to turn in corners, but the rear wheels of the Tesla Semi have been shielded to create a smoother airflow.
Should they stop there? Of course not! The trailer itself can be optimized a lot as well, with side skirts and flaps at the rear for example. There’s plenty of after-market equipment already out there. 

You can argue that in the end, it’s the CO2 emission per unit of cargo that matters and that the Semi’s longer cabin reduces the available cargo space in its wake. But then again, this depends on local regulations and it’s not a coincidence that the European Union is increasing the allowable length.
 
They have already triggered others to come up with innovative concepts, like the Ford F-Vision, for example.

Credits: 
Tesla: https://www.tesla.com/
Mercedes: https://www.mercedes-benz.com/en/
Ford: https://www.ford.com/

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Wouter Remmerie

Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#TeslaSemiAerodynamics #AirShaper #ArodynamicsofTrucks

Truck aerodynamics - Tesla Semi Explained

For more information, visit https://www.airshaper.com
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In this video, we’ll be discussing glider plane design.

This time we interviewed the people at Friendship Systems, our partner company specialized in variable geometries for flow analyses. 

They have developed an interactive 3D web app to design a glider plane. It includes a first theoretical indication on the aerodynamics after which the 3D model can be sent directly to AirShaper for a full-blown 3D flow analysis.

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#GliderPlaneDesign #AirShaper #FlowAnalysis

Airplane design #3 - Glider plane design

For more information, visit https://www.airshaper.com
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In this video, we’ll be discussing the basics of flight dynamics.

1. Introduction
To fly an airplane in a straight leveled line involves a horizontal balance between aerodynamic drag & thrust force and a vertical balance between aerodynamic lift and gravity. To make an airplane take off, follow curved trajectories and land, involves a whole lot more and is the domain of flight dynamics.

2. Roll, Pitch, and Yaw
The main parameters used to describe this three-dimensional orientation are the roll, pitch and yaw axes of the plane, all running through the center of gravity.

- The roll axis, also called the longitudinal axis, runs from nose to 
  tail.
- The pitch axis, also called the transverse axis, runs from left to 
  right.
- The yaw axis, also called the vertical axis, runs from top to 
  bottom.
 

Also important is the plane’s orientation with respect to the relative wind vector, which is the combination of the velocity vector of the plane and the wind vector. Around the pitch axis, this is called the angle of attack. Around the yaw axis, this is called the sideslip angle. 

3. Leveled flight
During a leveled flight, the roll, pitch & yaw orientation stay constant. To achieve this static balance, the moments around all three axes must be zero, otherwise, the plane would start to change its orientation. 
For example, if the center of lift of the main wings is not aligned with the center of gravity, this can generate a pitch moment causing the plane to tilt its nose upward or downward. To neutralize this pitch-moment, lift or downforce can be generated at the tail. Keep in mind that the location of the center of gravity can change between flights and even during flights due to changes in cargo and fuel for example.

4. Dynamic flight
During dynamic flight maneuvers, the airplane changes its orientation.

To climb or descend, for example, the elevators at the tail can be lowered or raised. This will cause the angle of attack to change which will affect the lift and drag that are generated on the main wings for example. Mapping & understanding the correlation between angle of attack and lift is crucial to understanding & optimizing flight dynamics.
   
To achieve this, you can perform a wind tunnel test during which you monitor lift & drag values while gradually increasing the angle of attack from the lowest to the highest value of interest. Such a sweep procedure can also be performed digitally by changing the angle of attack over a series of aerodynamic simulations.

5. Horizontal sweep
The results are curves that plot the lift and drag values versus the angle of attack. This is quite similar to the 2D airfoil curves we saw in earlier videos, only now it’s the lift & drag of the full plane, taking aerodynamic effects like flow around the fuselage and wingtip vortices into account. 

Here as well, very steep curves could indicate that the plane is very dynamic but more difficult to fly. Such crucial information can then be used as input for the flight control strategy. 

6. Vertical sweep
A similar approach can be applied to a yaw maneuver, where the rudder at the tail is used to turn the plane left or right. Sweeping the sideslip angle beta again results in changes in the forces on the plane. In this case, however, the lateral force is of particular interest, as a sideslip angle will generate a sideways push on the plane.  

7.
This is only the tip of the iceberg in terms of flight dynamics: much of the airplane maneuvers involve a combination of pitch, roll, and yaw. Side winds can have a tremendous impact as well. And the speed of rolling, pitching and yawing also generates additional dynamic forces and moments that play a big role.

That was it for this short introduction on flight dynamics. Thanks for liking, sharing and leaving your comments below the video, thanks for watching and see you soon! Bye-bye.

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #FlightDynamics #FlightDynamicsAirplanes

Airplane design #2 - Flight Dynamics

For more information, visit https://www.airshaper.com
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In this video on Airplane design, someone else will do the talking. 

Some time ago I met Yong Wook Sin who works at the Peugeot design center. 

As it turns out, even during his free time, he likes to create cool stuff, like a futuristic electric airplane. 

For the full interview, check out this link: https://youtu.be/h1j7D_f0JbU

He spoke about using CAD programs to make 3D designs for his ultralight solar plane and using aerodynamics to calculate the possibility of keeping the airplane in the air indefinitely.  

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it?

Check out https://www.AirShaper.com and see how easy it can be!
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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it?

Check out https://www.AirShaper.com and see how easy it can be!

#AirplaneDesign #AirShaper #PeugeotDesign

Airplane design #1 - A Peugeot Designer's Vision

For more information, visit https://www.airshaper.com
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In this video, we will explain how we teamed up with Bioracer to develop the next step in individual performance clothing for athletes.
 
Golf ball dimples:
First, let’s talk about why golf balls have dimples. Euh wait, wasn’t this about athletes? Patience, we’ll get to that in a minute!

Golf balls without dimples feature a laminar flow. As the air moves over the surface, a boundary layer of slower moving air grows thicker as it sticks to this surface. As soon as the flow goes beyond the halfway point and needs to contract, it becomes more & more difficult for the flow to stay attached to the surface and eventually separates. This creates a large wake behind the golf ball, which increases drag and slows it down.

When you apply dimples to the surface, or another way of increasing the roughness, the boundary layer becomes turbulent. It will mix with the surrounding air and retain more kinetic energy. This energy allows the airflow to stay attached further down the back of the golf ball, reducing the wake created in its path. These dimples may increase the friction drag a little but reduce the pressure drag so much that the golf flies roughly twice as far!
 
So does this mean we should cover every surface with dimples to make it more aerodynamic? Hm, not quite. Increasing surface roughness to create a turbulent boundary layer only makes sense in locations upstream of a location with separation. Otherwise, you’re only increasing the friction drag!

Cyclist flow
That being said, it’s time to move on to athletes. The flow around a cyclist, for example, is a complex combination of laminar & turbulent flows, that are attached in some regions and separated in others. So the location of where increase the surface roughness is critical.
 
Bioracer, a Belgian company that is well known for its high-tech sports clothing,  already offers clothing that features a smooth surface in some areas and a rough one in others. Like increased roughness at the upper arms for example, which are comparable to cylinders in shape and where it pays off to have the flow stay attached further down the back to reduce drag. 

Individual
This is not where it ends though: every athlete is different in terms of body shape and position on the bike. This means that the locations where the flow separates are different as well! To offer a highly individual approach to drag reduction, Bioracer and AirShaper went to the Bike Valley wind tunnel to experiment with roughness increasing materials in different locations.
The test specimen of the day was Ismaël Ben-Al-Lal, triathlete, and winner of the Taiwan Iron Man in his age group in 2018 and now prepping for the one in Hawaïi. After computing Ismaël’s aerodynamics using a 3D scanned model we uploaded to the AirShaper platform, we analyzed the results together with Bioracer. We sat down to define suitable locations for increased surface roughness.

For example, we didn’t make the entire surface of the upper arms rough, as is done on existing professional jerseys. Instead, we applied rough patches tailored to specific locations on Ismaëls arms & legs and the flow around them.

Over a series of wind tunnel tests, we indeed measured drops in aerodynamic resistance and we discussed possible layouts for Ismaëls next personal outfit. This simulation-based aerodynamics approach is our path towards highly individual performance equipment.

So that was it for this episode of custom aerodynamics! I hope you liked the video and if you have any questions, just leave them in the comments or get in touch with us directly to discuss your own project.

Thanks for watching, see you soon, bye bye!

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it?

Check out https://www.AirShaper.com and see how easy it can be!

#CustomAerodynamics #AirShaper #Bioracer

Custom Aerodynamics - Bioracer meets AirShaper

Aerodynamic clothing plays an important role in reducing drag and increasing the performance of an athlete. We teamed up with Bioracer and used CFD and wind tunnel testing to develop aerodynamically efficient cycling gear

The importance of aerodynamic clothing

For more information, visit https://www.airshaper.com
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In this video, we’ll take a look at smart mobility and the role of aerodynamics.

1. Some context:
According to the United Nations, 60% of the world’s population will live in cities by 2030. With cities already congested and polluted today, this poses a massive challenge to urban mobility.

So we’ll need to rethink the way we transport ourselves and goods, around & within cities as a whole, something called “Smart mobility”. We found many different definitions on this, so here’s our attempt to summarize it:

Smart mobility aims to use new technologies like:
1. high-speed data connections, 
2. self-driving tech, new materials & propulsion methods to create 3. sustainable mobility. And very likely, this will be a 
4. combination of different transport modes, like taking the car to the city to continue locally on the electric step, for example.

2. Weevil
To improve flexible & efficient travel between and within cities, a consortium of industry experts from around Europe have created the Weevil project.

The weevil is a highly innovative three-wheeler with two wheels at the front and one at the back. There is even room for 2 people in tandem position.

This car solves the contradiction of needing a wide wheelbase for stability in corners and a small wheelbase to maneuver in tight traffic and parking spaces. They developed a suspension mechanism that allows the front wheels to move outwards at high speed and inwards at low speeds. 

3. Aerodynamics
So practicality is covered, but what about efficiency? Of course, it’s electric, but you want to get as far as possible on a single charge. Or, make the battery smaller & lighter for a given range. In any case, reducing the energy needed to move around is key: even at intermediate speeds of 80 km/h, aerodynamic drag easily makes up for more than half of the power the battery needs to deliver.

4. The benefits
Luckily, having 2 people sit in a row rather than next to each other, greatly reduces the frontal area of the Weevil.

Another benefit of this setup is the possibility to give the car an aerodynamic drop shape, which closes behind the passenger, to reduce the wake.
 
And the rear wheel of the car is tucked away nicely at the end of this drop shape to prevent it from creating highly turbulent air as the rear wheels do on a normal 4-wheeled car. 

5. The challenges
Also challenging for small cars is the fact that some components don’t scale down like mirrors and door handles. So it’s quite a challenge to keep their relative contributions to drag low. And with variable front wheel track width, the suspension is exposed to the external air. Therefore, the Weevil team paid a lot of attention to limit the drag penalty in wide track mode.
 
6. The design
Packaging all of this together in a good looking car is not an easy task. Luckily, with Masato Inoue, the former Chief Designer of Nissan who designed the Nissan Leaf, and Hexagon Studio, transportation design & engineering experts, the Weevil team managed to turn this concept into a stunning city car.
And there is yet another cool link between the Weevil project and aerodynamics: 25 years ago, Alberto Morelli studied new ways to reduce the aerodynamic drag of ground vehicles. And today, it’s his son, Massimo Morelli, who is handling all communications concerning the Weevil project.
 
So that was it for this video! I’If you liked it, please click the like button below and if you have any questions or comments, just post them below the video!

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it?

Check out https://www.AirShaper.com and see how easy it can be!

#AirShaper #CityVehicleAerodynamics #SmartMobility

Smart mobility  - City Vehicle Aerodynamics

For more information, visit https://www.airshaper.com
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In this video, we’ll be looking at how to speed up the aerodynamic design process by working directly with open surface models!

Solid vs Surface models
First a few words on solid versus surface models.
In engineering, most 3D models are designed just like they are machined in real life: you start from a solid block and take away the excess material until you have the desired shape. It’s still solid on the inside and there are no gaps between the different outside surfaces.

In design or styling, however, 3d models are often built as a combination of complex surfaces: you start for example from a simple rectangular plane, which has two sides. Then you start pushing & pulling the different vertices on that plane until the shape looks good. To obtain the full 3D model, multiple surfaces are put together, sometimes overlapping, sometimes with gaps in between.

Watertight models
Now when it comes to aerodynamics simulations, it is typically required to work away all the gaps & interferences, to obtain something that is called a watertight or manifold 3D  model. In case of surface models, this often means weeks of model fixing to obtain a 3D file that is ready for simulation.
A trick to avoid remodeling is to use a wrapping method, which will literally wrap a closed surface around your model. But this can be quite tricky, as you may end up losing small details or closing holes & small gaps that weren’t supposed to be closed, like ventilation holes in a helmet for example.

Algorithms
The only proper way to avoid risky wrapping methods or weeks of remodeling is to accept the surface models as they are by treating every surface like a wall on both sides. That’s exactly what we do at AirShaper – we tuned our algorithms for months to make them work directly with open surface models. Let me show you an example of how this speeds up the aerodynamic design process:

 
In Practice
Auto Access is a company that develops & installs auto accessories, like for example hardtops for pickup trucks. In the light of more demanding emission regulations, they asked us to assess the impact on fuel consumption of adding a hard top to the Nissan NP300 pickup truck.
As you can imagine, Nissan doesn’t simply hand out their confidential 3D data. So instead we turned to a professional website for 3D car models. And as you may have guessed, these are all surface models with plenty of gaps and holes.

The results
So instead of closing all these holes, which would have required more budget and time, we just uploaded the model straight into AirShaper. Every surface was treated as a real wall on both sides. And although air leaked to the inside in some locations, these static pockets of air didn’t affect the overall behavior of the flow.
The result? Just a day after obtaining the 3D model, we were looking at the aerodynamic report. And the best news? Adding a hardtop to the Nissan NP300 doesn’t increase fuel consumption!
So that was it for this video, if you liked it, please click the like button below and don’t forget to leave your comments!

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!

Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it?

Check out https://www.AirShaper.com and see how easy it can be!

#AirShaper #AerodynamicSimulations #OpenSurfaceModels

Save weeks! Run aerodynamic simulations on open surface models

For more information, visit https://www.airshaper.com
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Some say…
That motorbikes where invented by car designers on half the budget,
And that secretly, they found driving on half the number of wheels twice the fun.
All we know is, aerodynamics make them both go faster!
 
Drag
But in case of a motorbike, it’s all a bit more difficult. Let’s start with the obvious:
Motorbike drag is a disaster: apart from some laminar flow around the front fairings, turbulence is king everywhere else. With open wheels, sharp edges and a driver shifting position every two seconds, it’s a challenge to bring down drag.
 
Over time, people have come up with all sorts of clever ways to shield & streamline the driver. But sidewind sensitivity and practicality are big concerns, as you can perhaps imagine.
 

Pulling wheelies
Obviously, drag can be overcome by more power. But with acceleration and drag both trying to flip you over backwards, they add up to make you wheelie even faster. And as cool as that may sound, it’s the sign you’ve reached your maximum acceleration rate. When you’re in a race, that’s not what you want.
So imagine there is something that could push the front wheel down onto the ground, that would help a great deal. That’s exactly why over the past years, Ducati and others have been experimenting with front wings on their bikes: although not much, they create downforce on the front wheel, counteracting the torque of acceleration and drag.

Cornering
The effect of downforce on cornering is a bit more complex though, as the aerodynamic vector tilts together with the lean angle of the bike: the downforce generates more pressure and thus more grip, but it also pushes you outwards. The net effect is only positive with a tire friction coefficient of more than one, or when the rider is leaning more into the corner than the bike itself, keeping the downforce as vertical as possible.

More power
So once you’ve found a way to put more down power, it’s a matter of generating more of it. But more power means bigger cooling demands, and more cooling means bigger radiators. Unless you can use them more efficiently.
Airflow through a radiator is generated by a pressure difference between front and back. Increasing this pressure difference increases the driving forces for this airflow and thus the cooling performance. Computational fluid dynamics simulations allow you to identify or even create a suitable high and low-pressure zone for this purpose. Typically the high-pressure inlet is located at the front of the bike and the low-pressure outlet located on the sides for example.
 
Comfort
Not all bikes are designed to go as fast as possible though: some are there to enjoy miles & miles of highway cruising. Just you, the road, and perhaps a bit of unwanted wind noise. Designing the front windshield and the shape of your helmet are crucial towards reducing noise levels. This noise is in part the result of the turbulent kinetic energy of the airflow being dissipated in the form of noise energy. Simulating the sound power generated in the airflow around the rider greatly helps to understand where this noise is coming from.
 
Heat
Another effect of this turbulence is the heat transfer rate: a turbulent flow is much more capable of transferring heat between the rider and the surrounding air. That can be good when you need some chill on a hot summer day but can make you freeze on a cold winter night.

And on that bombshell, it’s time to end this second movie on sports aerodynamics!
Thanks for watching and don’t forget to click the like button and leave some comments! See you soon!

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #SportsAerodynamics  #MotorbikeAerodynamics

Sports Aerodynamics #2: Motorbike Wheelies!

The physics behind motorcycle wheelies is surprisingly complex. Aerodynamics, downforce and drag can all play a crucial role in executing the perfect wheelie.

The aerodynamics of motorcycle wheelies

For more information, visit https://www.airshaper.com
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In this first video on aerodynamics in sports, we’ll have a closer look at how my mentor Ismaël Ben-Al-Lal is preparing for the Ironman in Hawaii in 2019, after winning the one in Taiwan in his age group in 2018.

Our partners for this video:
https://www.uantwerpen.be/en/
https://www.voxdale.aero/
https://www.linkedin.com/in/ismaël-ben-al-lal-0a55b021

Wind simulation by:
https://airshaper.com/

3D scan with:
https://www.artec3d.com/

First a short recap on the Ironman: you start off with a 3.86km swim, then you jump onto your bike for a 180.2km and you finish with a 42.195km marathon. Fair to say that every bit of reduction in resistance is appreciated during such a race.

It’s particularly important for the cycling bit: aerodynamics make up for over 80% of the total power you’re pushing through the pedals at 10 meters per second. So Ismaël got into the science behind it to go even faster. To do so, he got himself 3D scanned to obtain a 3D model for aerodynamic simulations. Here’s a short interview we did with him:

--- Interview Ismaël ---

To make the scan of Ismaël, we cooperated with engineering agency Voxdale and the product development department of the University of Antwerp. They used an Artec Eva 3D scanner that uses structured light to transfer Ismaël into the digital world. The total scan took less than 5 minutes to complete and with some post-processing, his body was isolated from the bike to focus on his body rather than his bike. Not that the bike and the body don’t interact aerodynamically, but sometimes it’s interesting to see what is possible without the bike.

So we pushed the 3D scanned model straight onto our platform for a Detailed Simulation and without revealing too much of Ismaël’s competitive advantages, we do want to provide two quick insights to get you started:
- First of all, the helmet. In the top view, we can see that Ismaël’s helmet is not oriented perfectly straight. This can cause unwanted drag, so be sure to turn your head straight into the wind. When there is a side wind, this may mean you’ll have to slightly rotate your head into the wind.
- Second of all, the upper arms: trying to keep your shoulders tucked inside could help reduce the wake just behind the top part of your upper arms. 

That was it for this first introduction to aerodynamics in sports. If you liked it, please click the like button and subscribe to our YouTube channel to stay tuned for more. And if you have any tips on other topics, just let us know in the comments!

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #SportsAerodynamics #IronmanTriathlon

Sports Aerodynamics #1: Winning the Ironman Triathlon

Optimising the design of an aero bike as well as rider posture is essential to reducing drag and saving energy. This energy can then be used later to race faster and longer, maximising athlete performance

Designing an Aero Bike to win the Ironman

For more information, visit https://www.airshaper.com
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In this video, we’ll be looking at what happens when we move to three-dimensional shapes.

For the full report of our Generic Drone Simulation, click here:
https://airshaper.com/assets/reports/AirShaper_sample_report_-_drone.pdf

To get started, let’s have a look at the aerodynamics of a fixed-wing drone. I have a simple 3D model that I’m uploading to AirShaper. I’ll just call it “GENERIC FIXED WING DRONE” and drag the STL file into the box. It’s a flying drone, so I’ll set it to “above the ground” and “moving” and give it a 15 m/s velocity. Now let’s rotate the nose forward and then pull it upwards, giving it an angle of attack of 15°. That’s not a very efficient flight regime, but it will allow us to see some more interesting flow results. The model was exported in meters and that’s it, now let’s order the simulation.

Ok, we’re back, 4 hours later and the simulation has finished. We’re interested in what happens at an angle of attack of 15°, which should cause a stall. But first, let’s relate to the drag & lift theory of the previous video. This drone has a lift of 21.61N versus a drag of 4.94N. That’s a lift-over-drag ratio of 4.37. Not very impressive, as we saw values of more than 100 in the previous video! Let’s have a look at some techniques to find out what is going on.
One way of finding sources of drag is to look at the total pressure coefficient. Plotting a 3D cloud of where this equals 0 is a good indication of where you have a wake or a draft zone, and thus a cause of drag. As we can see, the outer parts of the wings seem to cause quite a big wake.

To get more insight, surface streamlines & surface friction can help. Remember when we talked about flow separation and adverse pressure gradients? You can detect the edge of a separated zone by looking at low values of surface friction. Looking at the top of the drone, we can see that the outer parts of the wing feature such a separation zone. In that area, you can see the surface streamlines move in multiple directions, even opposite to the wind direction.

You can also see this reflected in the surface pressure map: for a wing to function properly, we need high pressure at the bottom surface and low pressure at the top surface. In this case, the air stays nicely attached to the centre part of the drone. High velocity, low pressure. But at the outer parts of the wing, the air separates right after the leading edge, rapidly increasing pressure and thus reducing lift.

Let’s build a few theories on why this happens. First of all, there is the airfoil that is used. At the centre, the airfoil has a high relative thickness. At the outer parts of the wing, the relative thickness is much lower. Airfoils with a high relative thickness tend to have a higher stall angle of attack. We can see this when comparing lift curves of the NACA006, NACA0012 and NACA0018, which are basically the same airfoil with a different thickness.

Another theory is the shape of this fixed-wing drone. It’s a blended wing body, with a triangular platform, the shape when viewed from above or below. The air first hits the bottom of the nose and is pushed sideways in the process. As it bends around the nose towards the top side, it is pushed back towards the centre by the surrounding air. As the left & right join at the top centre, they fill the wake that is there and prevent separation. This inward & upward pull of air towards the centre could increase the local angle of attack at the outer parts of the wings, triggering stall.

So then how do we prevent this? Well, the question could also be should we prevent this? We’ve deliberately triggered stall by setting the angle of attack to 15°, which is not a standard flight regime. We’ve also seen that stall only happened on parts of the drone, which can be a good thing: a gradual stall in function of the angle of attack will make the drone easier to fly at the limit for example, while it could still be very efficient at lower angles of attack.

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper
 
#AirShaper #DroneDesign #3DFlowAnalysis

Drone design #2: 3D Flow Analysis

The details of a drone design can signficantly affect it's aerodynamic performance. In this article, we use AirShaper software to analyseand improive the aerodynamics of a fixed wing drone

Drone design: 3D flow analysis

For more information, visit https://www.airshaper.com
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Drone types
Rotary wings, quadcopters, for example, use the vertical thrust of the propellers to keep the drone in the air. A fixed-wing drone, however, relies on conventional wings to generate the required lift, just like an aeroplane as it travels through the air. In most cases, this setup eliminates any hovering capabilities, but it greatly increases efficiency, giving you much longer flight times.
Fixed wing drones come in many shapes & designs. Some look just like minified aeroplanes, with a propeller at the front, a fuselage in the middle with a long slender wing at both sides and a tail with vertical and horizontal flaps. Blended wings, on the other hand, look very futuristic, with fuselage and wings morphed into a single piece, without any tail at all.

Airfoil basics
Whichever design you go for, you’ll need to choose some kind of wing section, called an airfoil, to generate lift. In more advanced designs, the size or even the shape of this airfoil can change along the width of the wing, but it’s always a good starting point to do some basic hand calculations first.
Let’s start with naming the basic parts of an airfoil. At the front, you have the leading edge, at the back you have the trailing edge. They are connected via the upper surface, also called the suction surface, and the lower surface also called the pressure surface.
The chord is the straight line connecting the leading & trailing edge. The camber line, on the other hand, runs nicely in between the upper and lower surface, showing the centre line of the wing. 
The angle of attack is the angle between the chord and the relative wind direction. The relative wind is not only composed of the wind vector but also the velocity of the drone itself.

Lift and drag
Essential to airfoils is how much lift & drag they generate. Lift is the vertical force perpendicular to the relative wind direction. Drag is the horizontal force along the wind direction. These vary in function of the angle of attack. There is a great website called http://www.airfoiltools.com/ that provides you with tons of data on different airfoils. To understand drag & lift curves, let’s illustrate this using a symmetric airfoil, where upper and lower surface are identical. An example is the NACA0012.
At zero angle of attack, the lift is zero as well. There is only drag. As soon as the airfoil rotates its nose into the air, creating a positive angle of attack, it starts generating lift. The bigger the angle of attack, the larger the lift. Beyond a certain critical angle of attack though, the lift will start to decrease again. This operating region beyond the critical angle of attack is called aerodynamic stall and is caused by a separating flow at the suction surface of the airfoil. Trying to pull up too fast during take-off, for example, is a typical scenario in which planes can go into the stall, lose lift and risk crashing. 

Another effect of increasing the angle of attack is the increase in aerodynamic drag, which could cancel out the positive effect of lift. To find the sweet spot, we can use the lift-over-drag curve, which plots the ratio of lift over drag in function of the angle of attack. The NACA0012, in this case, reaches its maximum efficiency at an angle of attack of around 8°. At this point, the lift generated by the wing is 80 times bigger than the aerodynamic drag!
This is not the best you can get through. In contrast to symmetric wings, asymmetric wings sacrifice performance at negative angles of attack to generate more lift and less drag at positive angles of attack or even at zero degrees. With airfoil tools, you can easily compare two different airfoils, like the symmetric NACA0012 versus the asymmetric NACA6412. You’ll see that the NACA6412 peaks at a lift over drag ratio of over 140!
As you may have noticed in these curves, lift and drag are expressed as coefficients Cl and Cd, rather than the real lift and drag force. This makes it easier to compare different airfoils, irrespective of their size. The coefficients are calculated by dividing the lift or drag per width of the airfoil by the product of stagnation pressure and the chord length.

For more information, visit:
www.airshaper.com
www.airshaper.com/race-car-aerodynamics
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #DroneDesign #AirfoilDesign

Drone Design #1 - Selecting an Airfoil

Selecting or creating the optimum airfoil design can be a signficant engineering challenge. AirShaper's guide below explains the theory behind airfoil design and the most important aspects you need to consider

Fundamentals of airfoil design and selection

For more information, visit https://www.airshaper.com
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DIY Aerodynamics #2: Vortex Generators


Volkswagen Beetle
You may remember one of our previous videos in which we analyzed the aerodynamics of a Volkswagen beetle, do it yourself style. We discovered that the airflow over the roof detached somewhere around the rear window. The theory was that the downward angle was too steep for the flow to stay attached.
Let’s dive into some theory on when this can happen.


Boundary layer
As air flows over a surface, it will stick to it, slowing down to zero. Away from the surface, air is moving at the free stream velocity.  In between the two, you’ll get a velocity profile. This transition zone is called the boundary layer.As the air in the boundary layer is moving slower, it contains less energy and less momentum than the faster air above.


Flow separation
If the curvature of the surface is too strong, the air in the boundary layer will not have enough momentum to follow it. The more energetic flow above will be dominant, wanting to continue on its horizontal course, pulling away from the surface causing the flow to detach or separate.
Locally, the velocity profile close to the surface can even feature a reverse flow, caused by an adverse pressure gradient, creating a rotating separation bubble. We saw this in our previous beetle test, where the tufts at the top of the window would move in the opposite direction, towards the roof of the car.


Drag reduction
This separated flow increases the wake behind the car, causing unwanted drag. So how can we reduce this effect? One way of doing so is by simply reducing the curvature of the roof and rear window. You can see this on modern, streamlined cars like the Mercedes CLA. Another way is to install vortex generators.


Vortex generators
Vortex generators are little devices that improve the energy and momentum transfer from the free stream air to the boundary layer, giving it more momentum to follow the curvature. A very simple example is small vertical planes, placed at a slight angle with respect to the airflow. As the air hits the front side of these planes, pressure increases. At the rear side, the pressure decreases.

As you may remember from our video on wingtip vortices, the air wants to skip from the high-pressure side to the low-pressure side, creating a vortex at the top of the planes. This will cause part of the flow above the vortex generators to dive downwards, carrying momentum into the boundary layer. It will become more turbulent, stimulating energy mixing between the free stream air and the boundary layer.


Field test on the beetle
So we installed some high-tech paper vortex generators on the beetle to see if it works. It turned out the distance between the vortex generators and the rear window was quite crucial, but after a while, we found a position that worked.


Results
By analyzing the movement range of each tuft, we were able to compare both setups.
Without vortex generators, the tufts near the top of the window featured a lot of movement and reverse flow caused by the adverse pressure gradient. With the vortex generators installed, the movement was much reduced and the reverse flow was eliminated. 


So that was it for this video! If you liked it, please click the like button and subscribe to stay tuned for more!

See ya soon!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #DIYAerodynamics #VortexGenerators

DIY Aerodynamics #2: Vortex Generators

Vortex generators re-energise the flow within the boundary layer to avoid separation. This article explains how they work and demonstrates how you could install these on your own vehicle to improve aerodynamic performance

How to improve aerodynamics with Vortex Generators

For more information, visit https://www.airshaper.com
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In this video, we will be doing High Tech aerodynamic field testing do it yourself style. We took a 1970s beetle and equipped it with little tufts. 


Tufts
Tufts are small bits of light-weight wire that can move along with the wind. They allow you to see the local orientation of the air flow.
If they stay still and stick to the surface, this indicates nicely attached air flow.
If they wiggle around in different directions, this indicates turbulence, often occuring in zones of detached air flow.


Testing on a '70s volkswagen beetle
We equiped the roof and rear window of a 1970 volkswagen beetle with tufts, all around 10 cm apart.
We're curious to learn whether the air flow will nicely follow the curvature of roof and rear window, or detach and become turbulent at a certain point.


Observations
- Front section of the roof: at the very front of the roof, just after the jump from the front wind shield, we saw a slightly more nervous movement of the first tuft.
Admittedly, the effect was not very pronounced.
The other tufts further down stream were all stable.
- Rear section of the roof: all tufts on the roof stayed nicely flat and stable.
- Rear window: intense, nervous movement of the tufts


Interpretation
We saw that at the front of the car, we had a little bit of turbulence at the first tuft. This could indicate detachment of the airflow, possibly because the flow needs to rise up and jump on to the roof. 
The sharp angle between front wind shield and the top of the roof could cause local detachment of the air flow.
Right after that first part, the flow re-attaches again and all tufts are stable until it reaches the rear window: likely, the downward angle of the rear window is too steep for the flow to stay attached. The air detaches and follows a more horizontal trajectory, somewhere above the rear window, causing flow recirculation in the area below.


With special thanks to
- My dad, for being the best Go Pro Mount alternative in the market
- https://www.bensound.com/ for providing us with royalty free music that's easier to listen to than just wind.


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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #DIYAerodynamics #VWBeetleAerodynamics

DIY Aerodynamics #1: a '70s VW Beetle

There are a variety of affordable and effective flow visualization techniques that you can use on your own car to analyse its aerodynamic performance

Flow visualization techniques for your car

For more information, visit https://www.airshaper.com/race-car-aerodynamics
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In this video, we will be discussing race car aerodynamics.

Frontal area
If you want to reduce aerodynamic drag as much as you can, you want to keep the frontal area as low as you can. That is why race cars are quite small & low, very close to the ground.
Click here to learn more on aerodynamic drag:
https://www.youtube.com/watch?v=DbIIw-WryHY

Front splitter
At the front, the air hits the car. This generates a high-pressure zone pushing onto the car, but also onto the front splitter. The front splitter is a flat plate in front of the car that feels and captures this high-pressure air and pulls the car downwards generating down force.

Dive planes
Dive planes are the curved planes at the front wheel arches. They make sure that the wind jumps up, pushing the front of the car downwards as a result.

Wheel arch ventilation
The front wheels rotate at a high velocity creating a high-pressure air zone. If you ventilate that high pressure air at the top of the front wheel arches, this will push down the front wheel arches, especially as this air collides with the incoming air in front of the car.

Top air intake
We want to make sure that we provide high-pressure air to the engine, because that increases the power output. We can do so by positioning the air intakes high above the car in the free stream of the air to provide good capturing of air when it hits them.

Rear wing
This wing is comparable to the wing of an airplane, only it’s flipped upside down to not pull the car upward but to push it downward onto the asphalt. You want to make sure that the wing is positioned high enough so that it is in the free stream of the air and not in the dirty, turbulent air that is generated by the air intakes or other geometry of the car upstream.

Diffuser
The diffuser is the part that improves the transition from airflow underneath the car to the wake behind the car. If done right, this can strongly accelerate the air underneath the car creating a low-pressure zone pulling the car downward onto the ground. Click here to learn more on how a car diffuser works:
https://www.youtube.com/watch?v=9UgacwMJpuk&t=64s

Aerodynamic balance
This is the ratio between the down force at the front wheels and the down force at the rear wheels. You can play with this a lot in function of the track you want to race at. It is important as it influences the car’s handling, for example understeer and oversteer.

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.airshaper.com/race-car-aerodynamics
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #RaceCarAerodynamics #CarRacing

Race Car Aerodynamics

There are many devices that make up a Race car aerodynamic package, including the front splitter, dive planes, air intake, rear wing and rear diffuser. But what are the most important ones?

What are the most important Race car aerodynamic devices?

For more information, visit https://www.airshaper.com
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In this video, we will be discussing Reynolds number and Turbulence. Two closely related items. 


The Reynolds Number
The Reynolds number provides the ratio between the inertia forces and the viscous forces of a flow. It is calculated by dividing the product of the flow velocity, characteristic length and density by the viscosity. You can see it in this formula (00:00:18).


Laminar flow
At low Reynolds numbers, the damping effect of the viscosity is larger than the inertia forces that want to disturb the flow: fluid particles move on steady parallel trajectories. It looks very clean, very orderly. And that's why we call this laminar flow. 


Turbulent flow
At high Reynolds numbers, the inertia forces are big enough to overcome this damping effect and you will start to see nervous movements of particles superimposed onto the main flow. The trajectories are no longer parallel but they feature many local direction variations and swirls within the flow. We call this turbulent flow.


Transition point
As the Reynolds number increases, somewhere between laminar and turbulent flow there is a transition point or transition zone. As density, viscosity and object dimensions typically stay the same within a certain case, this often happens as the velocity increases beyond a certain point, a critical point. 


Example
A well-known example of this is the flow out of a faucet. If you turn it open only slightly, you will see a stable, clear stream of water. Turn it open completely and you will see a nervous flow full of bubbles.


Practical use
So how can you use this Reynolds number in your own application?
Unless you are running a case that is exactly identical to one that has been well tested, you cannot compare directly.

Because the Reynolds number is a subjective thing, there is no clear definition of the characteristic length. It's more of a subjective method to characterize a flow rather than a real physical property. But by calculating the Reynolds number for your application, you can roughly compare to other applications, to get the first idea on whether the flow will be laminar or turbulent in your case. Using the Reynolds number you can analyze the flow of a scaled model, that you have tested in the wind tunnel for example, and extrapolate to a full size one. That's pretty useful for wind tunnel testing.


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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #WindTunnelTesting #ReynoldsNumber

The relation between Turbulence, Reynolds, and Wind Tunnel Testing

The Reynolds number is a dimensionless quantity that is used to describe the flow characteristics of a moving body of fluid.

How to calculate Reynolds number

For more information, visit https://www.airshaper.com
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In this video, we will be discussing wingtip vortices. I will explain how wings on planes & drones generate vortices. What is causing them? How do they impact flight times? And how can you reduce them using winglets? 

Introduction
Have you ever seen those upward sharky fins at the tips of an airplane wing? 
They are called wingtips and they are there to increase the performance of the wing by reducing the vortices. And it doesn't apply just to airplanes, but also to fixed-wing drones, wind turbine propeller blades and others.

What is a vortex
Simply put, a vortex occurs when the air rotates around a line in the air, like a tornado for example. But how are they created?
To keep an airplane or a drone in the air, it needs to generate lift. This can only be done if the total pressure at the bottom of the airplane is bigger than the total pressure at the top of the airplane, generating a net force upwards. 

But as nature is always looking for balance, the air at the high-pressure side, at the bottom, wants to skip over to the low-pressure side at the top.
Luckily there is a wing in between which then captures this force and generates lift. But at the tips of the wing, the air can bend around the tip with a 180° turn to skip from the high-pressure side at the bottom to the low-pressure at the top. 

So as this airplane travels through the air, it generates a continues swirl or vortex in the air. These wingtip vortices create a loss in lifting properties of the wing as part of the crucial pressure difference between bottom and top, is lost. 

Preventing vortices
Eliminating wingtip vortices completely is quite difficult, but you can reduce them by adding a little wall at the end of the wing (a winglet).
This will prevent the air from crossing over from the bottom side to the top side. 

So how big is this effect? 
How much can you gain by adding them? We've done a project specifically on drone winglets. It was a fixed-wing drone and it already had wing tips. By analyzing and improving them, we improved the lift over drag ratio by up to 30%. 
Which is quite massive for a fixed-wing drone.

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

 #AirShaper #WingTipVortex #WingletsPurpose

What is a Wing Tip Vortex?

Winglets are miniature vertical aerofoils located at the wingtips of airplanes, drones and wind turbine blades. Winglets reduce the strength of wingtip vortices, reducing drag and improving aerodynamic efficiency.

How do winglets improve aerodynamics?

For more information, visit https://www.airshaper.com
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Link to sample report: https://airshaper.com/assets/reports/aquilo.pdf
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In this video, we will be discussing car diffusers. How do they work? Why do car designers install them? How can you make one for your design?  

Theory - the Bernoulli effect
The Bernoulli effect states that if you follow an air particle along its path within a flow the energy density remains constant. This means that if one term goes up, another must go down. This means that for example, if the velocity increases, the pressure has to go down.

Relation to the car underbody
The car underbody is the bottom side of a car. At the front of the car, you have high pressure because the air collides with the front of the car. At the back of the car, the pressure is lower because the wake wants to pull the car backward. This pressure difference between front and back of the car is the driving force of the airflow beneath the car which is called the car underbody or car underbody aerodynamics.

Down force
Because this section is quite narrow, the air has to speed up and this is where the Bernuit effect comes in:
higher velocity, lower pressure, creating a suction effect pulling the car downwards.
For a sports car that's fantastic, it means more grip. 

Diffuser
This effect of accelerating the air below the car can be much improved by shaping the rear of the car underbody, by giving it a slight upward angle.
This improves the transition to the normal velocity of the surrounding air and it helps to fill the wake behind the car.
The result is an even bigger acceleration underneath the car with more downforce as a result. 

Design
So if you want to design a diffuser, the question is, how large should the angle be?
Too low and the effect will be too limited. Too high and the air will separate and not follow the geometry of the diffuser.
So much depends on local dimensions and aspect ratios.
An angle between 7 and 10° is considered quite a good starting point for your design. 

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #CarDiffuser #SportsCarDesign

What is a Car Diffuser?

A rear diffuser utilises the Bernoulli effect to accelerate airflow underneath a car. Find out how a diffuser works and how to design one to maximise your car’s downforce and aerodynamic performance.

What is a rear diffuser?

For more information, visit https://www.airshaper.com
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In this video, we will be discussing Drag Coefficients.
What are they? How can you calculate them? And most of all, how you can use them in your design process!


Theory 
Drag coefficients are used to calculate the hydrodynamic (in water) or aerodynamic (in air) force on an object, given the density Rho (ρ), the speed (u) and the frontal area (A) of an object. So if you know the force on an object at a certain speed, for example after a wind tunnel test, you can calculate the drag coefficient yourself using this formula. (0:28)

Once you know the drag coefficient for a certain geometry, you can calculate the force for different object sizes or different velocities
That is very useful for example when you need to size engines, calculate required battery capacity, etc.
But keep in mind that the drag coefficient can vary in function of the Reynolds number. So be careful with large extrapolations to other speeds, sizes or densities.


Practical use
A drag coefficient allows you to analyze the aerodynamic efficiency of an object, irrespective of its size or velocity. That makes it possible to compare a cyclist for example to a building. They are quite different, but still, they have a normalized aerodynamic coefficient.
It is also quite useful within a design process: when you are looking at different concepts for example for your new project or new vehicle, you can rank them according to their drag coefficient. Or you could get inspired by aerodynamic shapes coming from a completely different sector (Mercedes once had a car design inspired by fish!).


Typical Values
A drop shape, which is quite efficient, can have a drag coefficient as low as 0,05, whereas a building typically has one above 1. Lower means more streamlined. 
So if you are working on a drone that needs to fly as far as possible on a single charge or a cyclist that wants a higher top speed, you will want to reduce the drag coefficient as much as possible. 



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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #DragCoefficient #AerodynamicTheory

What is a Drag Coefficient?

Drag Coefficients (Cd) are used to quantify the resistance of an object as it moves through a fluid. They are a dimensionless quantity which allows aerodynamicists to analyse the aerodynamic efficiency of an object.

For more information, visit https://www.airshaper.com
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In this video, we will be discussing aerodynamic drag:
Aerodynamic drag is the force that you need to overcome, as you move through the air at a certain velocity. You will feel this for example when you ride a bike, because even at speeds as low as 20 km/h, the force that you need to overcome to push the air away, already accounts for more than half of the push that you need to deliver. In this video, we'll be looking at a speed skier to explain the two components of drag - pressure drag and friction drag.


Pressure drag
When the air hits the front of the skier, the pressure builds up, so that creates a force. At the back of the skier, air is dragged along, lowering the pressure, creating a wake (or draft zone) behind the object as well. If we integrate the pressure over the entire surface of the skier, we obtain the total force acting on the skier. If we want to know the drag, we just filter out the component of the total force that is directed along the wind direction: this is called the pressure drag.

Now if we want to learn more on which parts of the skier are contributing most to drag, we must zoom in and have a look at the local pressure. Clearly, the bigger the pressure, the more it can contribute to drag. But if the surface on which the pressure is acting is actually parallel to the wind direction, it doesn't impact the pressure drag. If the high pressure is, however, working on a surface that is perpendicular to the wind direction, like the front of the helmet or the hands, it does contribute a lot to drag.
To make things easier, we've multiplied this local orientation of the surface with the local pressure to give you an image that shows the direct contributions to drag. You will notice for example that the sides of the arms and the legs only show neutral green color, not contributing to drag. And that's it for the pressure drag.


Friction drag
Next to pushing and pulling on the surface, the air also slides across the surface. This generates friction forces, and although they are typically much smaller than the pressure force, they are relevant as well. In the case of the skier, they only contribute to 4% of the total drag.
If you visualize this, you again get a color map, which is called the friction map. It looks quite different compared to the pressure map. At the front of the helmet for example, where we had a lot of pressure drag, we now have almost zero friction drag, because the air comes to a complete standstill and so there is no relative velocity. On the other hand, where the air needs to curve around the sides of the object, air speeds up and there is a lot of local friction and thus a lot of contribution to the friction drag.

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Wouter Remmerie
Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week!


For more information, visit:
www.airshaper.com
www.facebook.com/AirShaper
www.linkedin.com/company/airshaper

#AirShaper #AerodynamicDrag #CFDTheory

What is Aerodynamic Drag?

Aerodynamic drag is the force an object needs to overcome as it moves through air at a certain velocity. Aerodynamic drag consists of pressure drag and friction drag.

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