AUDI R8 V10 plus: Advanced Aerodynamics Explained
The 2017 Audi R8 V10 plus is adorned with a carbon fiber wing, splitter and diffuser. But what to they actually do? Find out here
The 2017 Audi R8 was co-developed with the R8 LMS race car, and even shares 50% of its parts. I recently had the opportunity to spend some time in a R8 V10, and it was the 'V10 plus' model. This means 610 hp, 413 lb-ft of torque and a load of carbon fiber trinkets that are said to help with aerodynamic performance.
Fixed rear wings and front splitters are becoming increasingly common in modern performance cars. They are often sold as an optional extra 'pack' or are found on the most hardcore of model variants in a manufacturer's line-up. So after spending a considerable amount of time in Audi's most hardcore, road going R8, I thought that you would like to know how all of this stuff works.
Carving through a Californian canyon road, the R8's V10 screaming in my ears, I look to my wing mirror and see the V10 plus' fixed carbon wing. It follows the curve of the rear quarter as it tails off, and looks quite remarkable, but it got me thinking. It looks great, but does any of this aero stuff actually do anything?
Carbon fiber fixed Rear Wing
Let's start with the most obvious aerodynamic adornment of the V10 plus; the fixed carbon wing. The standard R8 comes with an adaptive rear spoiler. This means that a section of the rear bodywork that is normally flush, can extend to provide some downforce if and when needed. This is called a spoiler because it only has one control surface (the top when extended) and only spoils the air moving over it.
The V10 plus however, gets rid of the adaptive spoiler and goes for a fixed carbon fiber wing. This is called wing because it acts in the same way in which aeroplane wings do. Air travelling over the top of the wing travels at a slower speed than the air travelling underneath it. A law of physics called Bernoulli’s Principle states that air travelling faster has a lower pressure. So when the air is split over a car wing, a pressure differential is created, with lower pressure below the wing, and greater pressure on top. This pressure on top of the wing pushes the car down into the road surface, giving you more grip.
2D Computational Fluid Dynamics simulation of a rear wing
Take a look at this CFD simulation of a rear wing. The blue area is a low pressure area, and the red area is the high pressure area. As you can see with the most red section of the wing, the very front tip of is actually causing drag. This is why the drag coefficient for the R8 V10 plus is actually 0.02 worse off when compared to the base R8.
Angle of attack
How much downforce a wing produces depends on its angle of attack. This is an engineering term for the orientation of the wing. In general, the steeper the wing, the more downforce.
2D Computational Fluid Dynamics simulation of a rear wing with steep angle of attack
However, as can be seen in the CFD with a steep angle of attack wing, the more dowforce from a wing, the more drag.
Carbon fiber rear diffuser
Rear diffusers are becoming more common on road cars, but the vast majority don't actually do anything, and are there solely for style purposes. So how can we tell if a car has a functional diffuser or not? It's all about the underbody.
For a rear diffuser to actually do anything, it needs a completely flat underbody, and ideally, be very close to the ground.
Audi R8 V10 plus rear diffuser
Using the same principle as above - faster air has a lower pressure - having the underbody of a car completely flat creates another aerodynamic phenomena; the venturi effect. The venturi effect occurs when air is squeezed into a smaller area, causing the air to accelerate. This faster flow of air under the car creates a low pressure area, which sucks the car into the ground.
This is actually far more beneficial in terms of downforce than a rear wing. Think of the active area. There is a huge area underneath the car, all of which is sucking the car down into the ground.
So what about the diffuser?
The diffuser is there to carefully reintegrate this air from under the car with the air passing over the car. This smooth blending of the two air stream reduces drag and turbulence, meaning that you get a lot of downforce, with little drag.
Those vertical lines serve a purpose too. They are there to maintain a straight flow of air over the diffuser, optimising the efficiency of the diffuser.
The front splitter provides downforce at the front axle through a phenomena called 'air dam'. It splits the airflow at the front of the car, sending some underneath the car - to that flat underbelly - and the rest over the car.
As there is a front bumper in the way of the air flowing over the car, air gets trapped in an air dam, providing downforce.
Does this all do anything?
Many modern road cars have wings, splitters and diffusers, but they are just for show. Look at the angle of attack of a Honda Civic Type-R wing, and you will see is is very shallow, and the rear diffuser is not joined to a flat undertray.
Audi however, have used their knowledge of racing, and developed aerodynamic attachments that give useful downforce. How do we know its actually working? Well, their quoted drag coefficients are higher than the base car, which mean that drag is being produced by these things. And as we now know, drag is a byproduct of downforce.