Written by Megan Jenkins on May 23, 2019
April 27th, 2018
In an older Formula 1 workshop organized by SimScale, we conceptualized and simulated an F1 car. In the first week of the workshop, we were joined by special guest Nicolas Perrin, Head of Trackside Engineering at Manor F1 and President of PERRINN F1 Racing. Nic presented an excellent overview of the aerodynamics of the PERRINN F1 car, and graciously took a number of interesting questions as well.
The recording of the F1 workshop with Nicolas is available on YouTube, but we also decided to share some of his advice in an easy-to-read format. The following is a transcript of some of his comments and a Q&A session that followed.
What are we doing, as designers, when we’re getting the results from a CFD analysis? What are we looking for? Basically, we are trying to get some directions into which area of the car we want to improve, and we’re trying alternative solutions.
Typically, we are looking at pictures of the car, like on the screen (above), which is pressure on the skin of the car. We are also looking at the pressure and the velocity in the fields of the cars.
For example, this picture (above) shows the flow velocity close to the skin. So, it gives a good idea of how much energy and air velocity is going around different areas of the F1 car.
We can see in the blue areas that the air is actually slowing down a lot. There is not much energy left, and then it gets yellow to red zones, where the air is accelerating, and that is the drive behind the change in static pressure, which is then transformed into a force. This is what creates the pressure on the tires.
If we look at different views, the most interesting one is the bottom of the F1 car. This is what we don’t see from the outside when we look at the race on TV, but really plenty of what we try to optimize is under the car. The reason is the effects. It’s about managing the flow quality going under the car, starting from the front downstream going towards the diffuser area in the flow. Look at the areas where the flow is accelerating; that creates downforce in the front wing.
Then, we addressed some questions that were submitted by the attendees.
Do you have any advice for graduate engineers that want to get into motorsports?
Perrin: You know it’s an industry where you have a lot more people who want to get into it, than the number of opportunities. You have to find your way in—it’s not easy at the beginning. It’s about making sure what you want to do, keep your head, and grab the first opportunity, and once you are in, that you’re up to do a good job. Don’t get disappointed if the opportunity doesn’t arrive right away, but once it does, go ahead.
Since you have a lot of experience with CFD in F1 car design, how much is the difference between CFD and reality?
Perrin: There is a difference, you know a wind tunnel model is a model, and a CFD model is another model, and the wind tunnel model is different to the real F1 car as well, so there are always differences between models. But what I have to say is, from my experience, in the correlation—which is how close the CFD is to the real car or to the wind tunnel car—you can find differences, but in a localized area, and mainly on the contact patch of the tire on the ground and things like that. Once you know that you will decide your CFD extensively for some areas, and you will always have to validate and check on the real car, what you think is positive. But overall, I have to say that’s why the industry is moving more and more to CFD. The models are getting much better, and are getting good enough to develop an F1 car. It’s very good.
The simulation results you showed were of the whole car and not a symmetric wind tunnel?
Perrin: Yes, that’s right.
One user said that he would expect the flow to be symmetric. So why is it not? He saw some non-symmetric structures.
Perrin: I have to say, that person is a very good observer. But first of all, to develop the F1 car, we try to run a full car, purely because there are quite a lot of tests when we put steer angle on the car just to simulate different conditions. Obviously, we need a full car for these, so we tend to use a full car all the time, which obviously needs a lot more completing power. Moreover, the asymmetric structure of the flow comes from the fact that purely the modern wind tunnel has a slightly different flow, as you find that the convergence is not always going to the same states, especially near the wheel compact parties. And that in itself creates an asymmetry. But it’s quite realistic because you have to know that the flow is not static, even though if we are simulating a steady static flow, it’s obviously the turbulence which then creates these sorts of differences. This is another reason for simulating a full F1 car, you end up with an average false; basically, you simulate twice the same model, and that gives you a better average answer if that makes sense.
I saw engineers painted some flow visualization on F1 cars during testing, I guess some oil patterns. Can we view the flow of these patterns in CFD as well?
Perrin: Yes, absolutely. It is called the oil flow. It is a very useful tool for the designer or the engineer. Actually, the picture you can see (above) is exactly the same as we would do on the real car. When we put the oil on the car, the oil is filled with really tiny particles, and the air flow will push these particles and show you actually the part of the flow on the surface. One thing is to look at the direction of the flow locally, but the more interesting thing is to look at areas where the flow indeed passed. The rear wing is a good example, as it is very close to separating, because we run it at a very high angle, generating more downforce. If you go too far, the flow will actually separate from the surface and the oil will show you that. That is because, from a clean sort of path, a rail applies so that it will stop and it will become a messy sort of picture, and you can see exactly where the flow separates. That is why we use the oil flow, and in the CFD post-processing, we have the exact same oil flow so you can compare as well.
Can you please explain the aerodynamics of the Brabham fan car (below)?
Perrin: Oh, the classic car, the old car? It’s like a hoover which is purely just to increase this sort of ground effect on the construction level on the other car. This is something we are not allowed to do anymore, so we generate downforce from construction level of -1 to -2 static pressure on the other car. But if you are able to suck the air out of this region with this sort of banned system, then you can generate even greater construction levels of -4, -5 CP. That was the idea.
Would you see a time when wind tunnel testing is completely replaced by CFD simulation for a competitive team?
Perrin: In Formula 1 at the moment, no. But you have first of all that aircrafts, airliners are completely designed in CFD and then they test it the first time, full scale. Maybe a bit of wind tunnel, but they rely on CFD. For lower categories in motorsports, they stopped to rely on wind tunnel testing for cost reasons, and it works for them. And, actually, in LMP1 and in F1, there is an existing car that is only designed in CFD, so it’s coming. In Formula 1 it will come, but it is still sort of 50/50—50% wind tunnel and 50% CFD. Purely because of the model needs and the computer power. When we get cheaper computer power in the near future, CFD will start to overtake the wind tunnel, yes.
Does the software take into consideration the suspension movement and flex of wings, etc., when wind speed increases?
(Note from SimScale: The simulation we performed in this workshop definitively does not. It is just the flow analysis so basically all the boundary conditions are fixed, and there is no interaction between the fluid and the structural computed for.)
Perrin: Yes, that’s right. I mean the bodywork of the surface, the mesh, that’s what we have at the end. The mesh in CFD is not going to move; it’s not going to flex as we apply pressure to it because there is no setup structure behind. Basically, we set the wheel under suspension to the right position for certain ride heights and situations. The suspension is effective in the right location for the right conditions, but the bodywork is not going to flex. However, you can do another simulation, where you basically tweak your geometry to what your stress analysis has sort of simulated for deflection, and you will find that model stiff but effectively in flex geometry conditions, so that can give you an effect. We do that a lot in Formula 1, just to track effectively this sort of flexibility effect on the F1 car.
What is the minimum scale you can use in a wind tunnel for having a good correlation between CFD simulation and the wind tunnel results? You mentioned that there is also, that the wind tunnel models are smaller, didn’t you?
Perrin: Yes. Basically, in Formula 1 people run 60%. First of all, you are not allowed to run more than 60% just to reduce and control the cost. And you can run some things on 50%—that’s what we used to run before—but now it’s 60%. The accuracy of the model will go to the square of the size of the model, so you can imagine that 60% is much better than 50%. But the cost to actually build the model is also to the square or to the cube of the model because it will be dependent on the volume. So, all in all, to say that people run 60% is better accuracy, but you also need a bigger wind tunnel because you don’t want the walls to be too close to your model. That’s what we call the blockage, so that’s where we are.
Do you agree that FIA should ban wind tunnels?
Perrin: I don’t think we could ban things this way. Teams have invested in wind tunnels and these investments are for maybe 20 or 30 years, so you cannot ask a company to stop it now. It doesn’t make sense as a business. We have to respect that. I don’t think it’s a great idea, but I’m not sure the wind tunnels are going to disappear—not in the very short term. Long-term, however, with CFD, we won’t use wind tunnels anymore. What I intend to do, with the LMP 1 and maybe Formula 1, is to go directly from developing in CFD to build a full-size car, and validate aerodynamically the car on the race track and maybe do some final adjustments. But on the real car, that’s probably the most efficient way to do it at the moment, especially in LMP 1.
We at SimScale would like to give special thanks to all of the many hundreds of attendees of the Formula 1 workshop, and especially to Nicolas Perrin, from PERRINN F1 and Manor F1, for his insights into Formula 1 racing!
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