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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!


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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

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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:
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#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:
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www.airshaper.com/race-car-aerodynamics
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#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?

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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:
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#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

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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!


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 #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?

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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:
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#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?

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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:
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#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:
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#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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