197 Aerodynamics (CFD analysis)

[ttrw2]

Yep fantastic work @tomislavp4 ! I just had a look for any empirical data on radiator pressure drop, there's plenty - but most use a porous media with a resistance curve to model more accurately.

Any radius you can add to the leading edge of that 15mm thick splitter will increase suction there and improve flow quality under the car. If you use the scalar contour for Total Pressure you'll see the large separation coming off that splitter at the moment.

 

[tomislavp4]

Yep fantastic work @tomislavp4Any radius you can add to the leading edge of that 15mm thick splitter will increase suction there and improve flow quality under the car. If you use the scalar contour for Total Pressure you'll see the large separation coming off that splitter at the moment.

I will try rounding off the leading edge and see what happens, thanks for the suggestion. I'll also test raised center sections although prototype aerodynamics have little in common with our cars as their splitters aren't really splitters but inverted wings in ground effect.

 

[tomislavp4]

I haven't done any CFD runs lately but I've done a few runs in a laptime simulation software to see how much of an effect the added downforce has around the track. For this, I'm using OptimumLap which is a free software that models the car as a single particle going around a flat track. It takes into account the mass of the car, power and torque curve, gearing, drag and downforce coefficients and tyre grip. It doesn't take into account center of gravity, weight transfer, suspension kinematics etc.

First, I did a simulation around Spa. The stock car does a lap in 3:17.3 minutes, the car with the cup spoiler is actually slower, by 0.5 and the lowered car is faster by 0.5 seconds. The car with the spoiler is slower because of the added drag which makes it struggle achieving high speed on the straights as illustrated by the left chart below, even though it does have higher grip in corners due to the added downforce as shown in the cart on the right.


Now Spa has fairly long straights where lower drag is important so I did a run around Cadwell park as well. The lap time for the stock car is 1:58.5. The car with the spoiler is 0.01 seconds faster and the lowered car is the fastest again, this time by 0.2 seconds.


This illustrates two points. First of all, adding downforce doesn't always make a car faster around a track because it also adds drag. The added drag can slow the car more then the downforce makes it faster, especially true for cars that lack power. Second, the bang for buck ratio for aerodynamic parts is much lower compared to that of other mods like tires and suspension stuff. For example, switching to semi slick tyres reduces the lap time around Spa by 4.6 seconds and around Cadwell by 2.9. To get the same effect from aerodynamics, you'll have to increase the downforce five times without increasing the drag!

 

[Cossers]

Just as a matter of intrest, the pic/simulations on the first post, have you any higher res images of the second one with the red background? I've an idea for a pic for the man cave! It's so cool looking.

 

[tomislavp4]

Just as a matter of intrest, the pic/simulations on the first post, have you any higher res images of the second one with the red background? I've an idea for a pic for the man cave! It's so cool looking.

No, I don't but I can make one when I get home

 

[Cossers]

No, I don't but I can make one when I get home

Nice one, no rush, just would like a good resolution pic so I can get a decent print from it

 

[tomislavp4]

Nice one, no rush, just would like a good resolution pic so I can get a decent print from it

Is 9000x5000 px enough?

 

[Spect]

This thread is epic!

 

[strell]

Yeah as above. What a good find and read this has been this morning!

 

[Marsch]

The simulations and aquired data is quite interesting and the findings in for example the relation to the spoiler are actually coinciding with what the teams racing Clios in the Nürburgring endurance series are reporting. Which is that the Cup spoiler or spoilers in general don't add anything when it comes to handling but only cost top speed.

But there's one thing I'd like to mention and maybe have a discussion about. It's the side vents or extractors as Renault calls them. According to their drawings they're extracting heat from the engine bay.

I saw pics with removed archliners that showed some kind of plastic wrapped cushions that are actually blocking at least direkt airflow from how it looked but I'd actually say that you can feel heat (warmer than outside temperature air) coming out of the vents under certain conditions (hot engine) but I'm not definitely sure about this and it's very well possible the hot air I felt comes from elsewhere like the brakes for example. The cushions are the reason why I've heard the opinion that the whole side vent thing is fake and just for the looks. Does somebody in here know more about this matter?

Sidenote: About the cutouts in the rear bumper. From all I know it's mainly done for the looks but should also help with dissipating heat from the brakes. I'm not aware that anybody ever reported a positive effect when it comes to aero.

 

[Liam Gunby]

This thread is awesome. Some serious time and effort has gone into all of that, so thank you for sharing it all with us! Its really good to know some of the actual science behind it. And as much as most of us probably already know most of the stuff we do is actually just for looks and not shaving 0.02 off a lap time, its really interesting to read it all!

 

[deekay16v]

Yep. Awesome thread. Thank you guy for your work. Wonder how RS200 is different to RS197, having that fancy inbuilt front splitter.

 

[Don Hogg]

The simulations and aquired data is quite interesting and the findings in for example the relation to the spoiler are actually coinciding with what the teams racing Clios in the Nürburgring endurance series are reporting. Which is that the Cup spoiler or spoilers in general don't add anything when it comes to handling but only cost top speed.

But there's one thing I'd like to mention and maybe have a discussion about. It's the side vents or extractors as Renault calls them. According to their drawings they're extracting heat from the engine bay.

I saw pics with removed archliners that showed some kind of plastic wrapped cushions that are actually blocking at least direkt airflow from how it looked but I'd actually say that you can feel heat (warmer than outside temperature air) coming out of the vents under certain conditions (hot engine) but I'm not definitely sure about this and it's very well possible the hot air I felt comes from elsewhere like the brakes for example. The cushions are the reason why I've heard the opinion that the whole side vent thing is fake and just for the looks. Does somebody in here know more about this matter?

Sidenote: About the cutouts in the rear bumper. From all I know it's mainly done for the looks but should also help with dissipating heat from the brakes. I'm not aware that anybody ever reported a positive effect when it comes to aero.

Yeah! great thread! I'm also wondering if anyone has opened up the side vents?

 

[Counterdoc]

Very interesting thread with nice simulations! Currently I am also simulating some aero options for my asphalt rally clio. Opening the side vents and putting openings in the rear bumper will be part of the simulation.

 

[M154MATT]

Love this sort of thread it calms my inner car geek. Top work!

 

[bedoef]

@Counterdoc looking forward to your findings!

 

[Spect]

@Counterdoc Looking forward to hearing your results soon. Thanks for sharing.

 

[Counterdoc]

Just wanted to give you an quick update. I am still on it. Need to modify the body to get a proper mesh for simulation. The current one is crashing during the calculations. Unfortuantely very time consuming but I need to get it working this month as I also need to build all those parts from carbon fiber until the season starts end of february.