AirShaper

For part 2, check this link: https://youtu.be/2W5Q2mllmxI
For part 3, check this link: https://youtu.be/0jOAAZOvSuM

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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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

Airplane design #1 - A Peugeot Designer's Vision

For part one, check this video: https://youtu.be/DqlDpUFcScc

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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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

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

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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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

Smart mobility  - City Vehicle Aerodynamics

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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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

Save weeks! Run aerodynamic simulations on open surface models

For more videos on motorbike aerodynamics:
- AMA superbikes: https://youtu.be/qrH_QBOrqbw
- MV Agusta - MotoGP - part 1: https://youtu.be/BUkaejkHRn8
- MV Agusta - MotoGP - part 2: https://youtu.be/fGNdMaVft_w
- Damon motorcycles - electric motorbikes: https://youtu.be/asYdvFfzHTs

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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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

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 part 2, check this link: https://youtu.be/A0Gx-lBzSFA

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.

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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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

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 part 1, check this link: https://youtu.be/kAXN3MlQxxc

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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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

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 part 2, check this link: https://youtu.be/FZHYcqRcDJM

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.


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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!

For more information, visit www.airshaper.com

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

DIY Aerodynamics #2: Vortex Generators

DIY Aerodynamics #1: See this link: https://youtu.be/CGmqdXKgBiQ


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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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).

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