Race car aerodynamics #3 - Aero mapping

For more information about race car aerodynamics:

In this video we’ll explain how you can build aero maps for your own race car.

What are aero maps?
In general, 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?
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
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.

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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!

[AirShaper]

Are you building your own race car, aero maps or CFD simulation setup? Just drop your questions & comments below!

[erikhein]

Should drag be taken into account when finding the aerodynamic balance to get as accurate results as possible? As we've done it, it's just the downforce of all the aerodynamic elements multiplied with their respective moment arms.

[MBTIMemes]

I don't even have a drivers license, why am I watching this ??
How did I even end up here?

[Edit:] It's quite interesting tho

[la]

Apart from sports cars & lorries, can aerodynamics help with normal road cars going in city traffic low speeds? how can one use external aerodynamics principles to make life of a common man better. I enjoyed the blog on indian rickswaw aerodynamics in the website, but I guess for road car OEMs it's not worth investing in aero . Can these principles used in future to make larger impact on people life?

[patrickbradford]

Where did you get the model? I can't find free versions anywhere.

[prasadchettiar]

hii your videos were great. Do we perform cfd of a vehicle while cornering? if yes what all condn are used