Aerodynamics of PERRINN F1 Race Car: Q&A with Nic Perrin
Q&A with Nic Perrin – from SimScale’s Formula One Workshop Series Session 1 on the Aerodynamics of the PERRINN F1 Race Car
In March and April, SimScale hosted a Formula One Workshop Series, where we conceptualized and simulated a F1 race car. We wish to thank all the attendees that made it so successful!
In the first week of the workshop series, 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 video replay of the workshop with Nic is available on YouTube, but we also decided to share some of his advice with you in an easy read. Following is a transcript of some of his comments and a Q&A session that followed.
Nic Perrin’s comments about the aerodynamics of the PERRINN F1 race car
What we are we doing when we are getting the results from CFD just as a designer? What are we looking for? Basically, we are trying to get some directions into which area of the car we want to improve, and I’m 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, and we are also looking to movies showing the pressure and the velocity in the fields of the cars, so I’ll show about quickly as well.
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 car.
We can see in the blue areas, the air is actually slowing down a lot. There is not much energy left, and then it got yellow to red zones, where the air is accelerating and that is the drive behind change in static pressure which is then transformed into a force, and this is what creates the pressure on the tires.
If we look at different views the most interesting one really is the bottom of the 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 again is because of 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. As you can see 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 to graduate engineers that want to get into motorsports?
Nic Perrin: You know it’s an industry where you have a lot more people that want to get into it, than the number of opportunities. So you have to find your way in, it’s not easy at the beginning. So it’s about making sure what you want to do and 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 it doesn’t arrive right away, but once the opportunity comes go ahead.
Since you have a lot of experience in CFD in Formula 1 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 car as well, so there are always differences between models. But what I have to say is, from my experience, in the correlation or what we call correlation (which is how close the CFD is to the real car or to the wind tunnel car) you can find differences. But in localized area, and mainly on the contact patch of the tire on the ground and things like that, so once you know that you will decide your CFD extensively for some areas, and you always will 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 a car. It’s very good.
The simulation results you showed were simulation 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 symmetric? Because 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 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. So obviously we need a full car for these, so we temp to use a full car all the time which obviously needs a lot more completing power. But the other thing is that the asymmetric structure of the flow comes from the fact that purely the modern wind tunnel has slightly different flow. Because 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 asymmetric. 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. Which is another reason for simulating a full car, because 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, so 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. So first, 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, the rear wing is very close to separating, because we run it at a very high angle, generating more downforce, but if you go too far, the flow will actually separate from the surface and the oil will show you that. 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. So 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 air out of this region with this sort of banned system than 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. Not just now, but you have first of all that aircrafts, airliners are completely designed in CFD and then they test it 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 because it is 50% wind tunnel, 50% CFD. Purely again 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 us at SimScale: the simulation we performed in this workshop definitively does not. It is just the flow analysis so it is 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 body work 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 on 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 body work is not going to flex. But 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 that model stiff but effectively in a sort of 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 car.
What is the minimum scale you can use in a wind tunnel for having good correlation between CFD simulation and the wind tunnel results because you mentioned that there is also, that the wind tunnel models are also smaller, aren’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. I think at the moment teams have invested in wind tunnels and these investments in wind tunnels are for maybe 20 or 30 years so you cannot ask a company who has invested in wind tunnels for 5 or 10 years ago to stop it now. It doesn’t make sense as a business. So we have to respect that. So 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. But long term, with CFD we won’t use wind tunnel anymore. And I intend to do, with the LMP 1 and maybe Formula 1, 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 that you will need. 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 wish to give a special thanks again to all of the many hundreds of attendees to the Formula One workshop series, and especially to Nic Perrin, from PERRINN F1 and Manor F1, for his insights into Formula One racing! Stay tuned for more of SimScale’s simulation for F1!