AirShaper

For more information, visit https://www.airshaper.com or email info@airshaper.com
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Also check out Fluid Mechanics 101:
https://www.youtube.com/channel/UCcqQi9LT0ETkRoUu8eYaEkg

On Aidan's channel, you can also find the uncut, full length video of this interview:
https://youtu.be/Ntl15C2KXCQ
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For this video, we interviewed Aidan Wimshurst, who did his PhD at Oxford University (United Kingdom) on Tital Power Generation.

Concept
Tidal currents originate because of the tides: as water levels change, water flows from one area to another. When the water needs to fit through a narrow channel or move around certain coastlines, flow speeds can be quite high. These streams are very predictable, which makes it much easier to integrate the energy they produce into the grid.

The general idea is to take a typical 3-bladed wind turbine and put it under water. But there are a number of key differences to wind turbines that make tidal turbines unique.

Wing tip vortex
On an airplane, the air at the high pressure location below the wing wants to move to the low pressure location at the top of the wing via the side (the wing tip). This creates a curling motion called wing tip vortex.

On a turbine, this vortex also exists but it leaves a spiral trace instead of a linear one. And this increased vorticity & turbulence can impact turbines further downstream. It also represents efficiency losses for the turbine itself, which is why some (wind turbine) blades are equipped with winglets.

Cavitation
If pressure is reduced below the vapor pressure, you will start getting bubbles. When these implode, they can cause serious damage to the blades, structure, and so on. The risk of cavitation is reduced when the hydrostatic pressure is high, close to the sea bed. But close to the surface, this hydrostatic pressure is much lower, increasing the risk of cavitation. So the risk of cavitation varies along a single revolution.

Farm layouts
For a given plot of land, the goal is to maximize energy and thus put as many turbines as possible in place. But if you put them too close to each other, the turbulent wake of one turbine will lower the efficiency and lifetime expectancy of other turbines, so there is an optimum to be found.

With tidal energy, the orientation of the flow is always the same, only changing direction between tides. So these are typically placed in an array. The flow around a turbine is accelerated, meaning that a turbine placed in this accelerated flow will yield more power, ánd the original turbine will also perform better. This is called constructive interference. This will be analyzed in the MeyGen project.

Size trends
Compared to wind turbines, the constraints are different for tidal energy. The water depth is typically between 20 and 50 meter, so that limits the rotor size. Also, the velocity shear (difference between the velocity at the bottom and free water surface) poses strong bending loads on the rotor.

Suitable sites
Tidal energy will never be able to provide the full energy demand of a country, but it can provide a valuable contribution. And it's also very useful for remote sites, which are typically islands, as they have difficult access to other sources of energy.

Tidal Stream Turbines - Renewable Energy from the Tides

For more information, visit https://www.airshaper.com or email info@airshaper.com
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For this video, we interviewed Derek Dorresteyn, CTO at Damon Motorcycles (https://www.damon.com).

Hyperdrive platform
The case of the battery is the main stressed component of the motorcycle, which means they got rid of the traditional motorcycle frame. It has reduced mass, the stiffness can be tuned and it provided more room.
Higher top speed, faster acceleration and far less rotating mass compared to an ICE motorcycle. It’s a really simple motor-gear reduction and this reduction in rotating mass significantly reduces the apparent mass, which otherwise adds forces that resist the vehicle leaning over and changing direction. Without the added forces, the bike feels much lighter in corner transitions.

Cooling
The electric drive train is far more efficient: 85% efficiency for the electric drivetrain versus 30% efficiency for the internal combustion engine. But the threshold temperature of a battery pack is much lower than that of a combustion engine, which again increases the required size of the radiator. Both more or less cancel each other out, meaning you end up with more or less the same radiator size.

Range
There is a lot of variability in the shape and size of the people that will be on the motorcycle, but also the way they interact with the bike can be different. For the optimization work in terms of drag, they have used a standard rider in terms of height and mass combined with the SAE J2982 drive cycle.

Aerodynamics
If they made a vehicle with the lowest possible drag coefficient, it likely would not be very commercial. So they have this tension between current design trends, consumer taste and the desire to improve aerodynamic performance.
The aerodynamics are extremely important: if they wouldn’t care at all, the range would just be half of the claimed 200 miles.

How to Design Electric Motorbikes - Interview with Damon Motorcycles

For more information, visit https://www.airshaper.com or email info@airshaper.com ----------------------------------------------------------------------------------------


In this video, we’re going to improve the aerodynamics of America’s favorite pickup truck, the Ford F150. As a starting point, we used a highly detailed 3D scan of the latest version of the 2021 Ford F150, here in its hybrid version, provided by our partner A2MAC1. We uploaded this 3D scan directly to AirShaper, set the speed to 30 meters per second, added rotating wheels and launched a Regular Simulation.
A few hours later, we could immediately spot a number of problem areas in terms of aerodynamics:
- Right after the cabin, the flow separates and turns into a turbulent wake. Some of the flow tumbles down into the cargo bed and then hits the tail gate on the way out, again creating a wake.
- The huge mirrors are without a doubt very practical and safe, but they also generate a lot of drag.
- The underbody features many exposed components. That’s very practical for easy access and quick repairs, but it strongly obstructs the flow underneath the car, which creates resistance.
- The wheels look nice, but with their sharp edges and large openings, they create what is called ventilation drag – it’s the energy lost on mixing the air, which translates into extra drag. Also, they create dirty air which affects the aerodynamics of the car further downstream.
- The ride height of the car is quite high – great for off-roading, but usually not so good for the aerodynamics of a car, as more air is now travelling through the channel between the underfloor and the ground. And with the underfloor being so exposed, this can also create extra drag.
The verdict: a drag coefficient of 0.463. Not very impressive compared to for example the 0.21 of the Lucid Air.

So, the guys at A2MAC1 went to work, drew inspiration from the Tesla Cybertruck and came up with a number of improvements – let’s check them out and see how much they each reduce drag!
- First, the rear cover: by closing the cargo bed, the flow across and around the cabin now stays largely attached to the rear cover. The air is prevented from hitting the tailgate and now nicely slides downward to help reduce the wake behind the car. This solution alone lowers the aerodynamic drag by a staggering 14.82%! Optimizing this global shape of the car helps to improve what is called the pressure recovery: at the front of the car, the air hits the nose and creates a high pressure, pushing the car backwards. Once it has crossed the mid-point of the car, the flow starts to contract again. If you support the airflow in the right way, this helps to create a forward push, compensating for some of the drag at the front. The base shape of the Tesla Cybertruck offers a lot of potential in this regard, although the sharp edges might need to be tuned a little.
- Secondly, the F150 was given a smooth underfloor. This is something we also saw when we analyzed the Porsche Taycan and which applies to many electric vehicles: because of the electric drivetrain, it’s possible to create an almost entirely flat underfloor. This facilitates a much smoother and less turbulent airflow which strongly lowers the drag. In this case, a very crude underfloor design already lowered drag by 3.4%!
- Then, the aerodynamic wheel covers of the Tesla model 3 were pulled from A2MAC1’s database and, after some stretching and scaling, applied to the Ford’s wheels. Without any optimization, these cut drag by 2.23%.
- Another tweak meant taking off the side view mirrors altogether. Yes, in reality you’d have to put camera’s instead, if regulations allow it at all. But just to show the potential, we ran a simulation and noted a 5.5% drop in aerodynamic drag!
- Last but not least, the truck was lowered by 2 inches – this is a trick some other cars already apply to lower drag at cruising speeds. In this case, it lowered drag by another 2%. 

When adding all of these modifications at the same time, we observed a total reduction in drag of 25.05% - that is a massive difference! If we assume that aerodynamics are responsible for roughly half of the energy or fuel consumption of a car, then this means a 12.5 reduction in fuel consumption, or roughly 12.5% more range!

Of course, all of these modifications have consequences towards practicality, safety, aesthetics and so on. But all of them have either already been applied or will be applied on upcoming cars.  And some tricks, like the underbody, may already be applied to the electric F150 lightning.

Ford F150 Aerodynamics - How to add more than 10% range!

For more information, visit https://www.airshaper.com or email info@airshaper.com
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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

For more information, visit https://www.airshaper.com or email info@airshaper.com
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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

Golf balls have dimples applied to their surface to manipulate the behaviour of the boundary layer to reduce the wake and overall drag. However, it only makes sense to use dimples just ahead of the separation point.

What is a Boundary layer?

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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

For more information, visit https://www.airshaper.com or email info@airshaper.com
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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

For more information, visit https://www.airshaper.com or email info@airshaper.com
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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!

Our Latest Videos Gain aerodynamic insight by watching our videos

Tidal Stream Turbines - Renewable Energy from the Tides

How to Design Electric Motorbikes - Interview with Damon Motorcycles

Ford F150 Aerodynamics - How to add more than 10% range!

Flow Separation - Boundary layer separation explained

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

Soccer aerodynamics - How to curve a ball

Porsche Taycan Aerodynamics Part 2: Road testing

Porsche Taycan Aerodynamics Part 1: aero features explained

Pitot Tubes - Measuring Flow Velocity

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