Aerodynamics (and CFD) of Cornering Vehicles

[argi2007]

Hello everyone,
i m studying mechanical engineering in Greece and i want to join my Formula Student team. I am interested in Aerodynamics so i started to look for information in various books and sites and i managed to do some basic CFD simulation (ahmed body) with fluent. What i have found particularly difficult was to gain some insight into the Aerodynamics of a cornering vehicle. Since the primary effect of downforce is to increase the speed in a corner, one would think that all the analysis and simulations should've be done with that in mind. So how one could do a CFD analysis of a cornering vehicle? Are there any books or technical papers related to this subject?

Thanks in advance

[Jersey Tom]

You could start by putting the velocity of the airstream at a yaw angle to the centerline of the car.

Better yet would be taking a step back and asking whether you really need to do that or whether straight line CFD will get you the answers you need.

Going with the most simple analysis that will get you an accurate enough answer is the way to go, IMO.

[Greg Locock]

In the absence of cross winds or other complications, the air velocity is generated by the forward motion of the vehicle, modified somewhat by the vehicle sideslip angle, which in a high speed corner is going to be a very few degrees only. Another way of thinking about is to tie a pretty pink ribbon to the nose of the car of your favorite driver, which direction would it point?

damn, tom beat me to it.

[argi2007]

Thank you guys for your quick response

According to this http://www.thinkflip.net/aerodynamics-o ... g-vehicles a 24% increase in drag occurs any comments?

[Lycoming]

well, three things:

1: He doesn't present any additional information to go along with that 24% number (speed, path radius, turbulence model, etc). I'm sure he has all of that information somewhere but the 24% number itself, presented without any additional information, is basically meaningless.

2: He basically has no way of empirically validating his CFD results. So, we have no idea if his CFD model correlates with reality at all. Not yet, anyways; it looks like figuring out a good way to do exactly that is the point of his doctoral dissertation.

3) There's no mesh sensitivity study. At least, there is none presented on that page, I would presume that has been done at some point. But basically, that page doesn't tell you anything about the mesh used for the bluff body model, nor do you know if the mesh is adequately refined.

With that said, everything I've seen suggests that the effects of cornering on the flow of the vehicle is very significant. But that's not saying much.

[thisisatest]

I do like the idea, on paper at least, of using models that have a slight bend in them.

[marcush.]

sure a straight on or in yaw and maybe vehicle roll inclination approach will get you somewhere ...but in my view this all is only aimed at reproduceability of test results in a controlled environment nothing more really.

It´s for good reason that some teams experience a lot of cross side and backwind sensivity on the track when others seem to be not affected at all ...simple..they do not take this into account when doing their aero work so your design may or may not be more vunerable to these effects than others designs.

I wonder if the aero design process is steered with requirements other then regulations and lift drag ratios and trying to machieve downforce levels you think are necessary to be competitive (and obviously balancing the cars aero).

The teams to some straaight line testing but this seems also just a correlation thing..as you are not really interested in these figures( aero downforce is just important when the car is under braking and in all other straight ahead situationss you don´t want a wing at all).So is this simplified model really a help if you are looking at those events that seem to depend on really small alterations or is it more you are establishing desired flow patterns and concentrate also on regression testing when you think you got a good solution.

[Jersey Tom]

Thank you guys for your quick response

According to this http://www.thinkflip.net/aerodynamics-o ... g-vehicles a 24% increase in drag occurs any comments?

Well, does your racecar look like a brick?

[argi2007]

[

Well, does your racecar look like a brick?

No it doesn't i made a search on the subject and i just found that, if you can find an analysis with a proper racecar you can post it right here.

[Jersey Tom]

[

Well, does your racecar look like a brick?

No it doesn't i made a search on the subject and i just found that, if you can find an analysis with a proper racecar you can post it right here.

I suspect that would be hard to find. And best practice is to question and verify any study or report you come across, unless it's from an extremely reputable source. And even then...

You might want to start simple and just look for anything you might be able to find with respect to airfoils in yaw. That and do your own CFD study on something simple.

Doing full vehicle CFD at various front and rear ride heights is probably going to be challenge enough without throwing in varying yaw angles as well. Keep it as simple as you can get away with...

[TotalSim]

You could try something along these lines

http://www.totalsimulation.co.uk/wp/cor ... -openfoam/

Good luck.

[MadMatt]

Being the rally guy that I am, please consider the high vehicle side slip angles encountered in rallying during sliding (which occurs a lot), and its impact on vehicle handling. For circuit racing I wouldn't bother, that's for sure. More gains to be made by refinement before going to full models with yawed flow domain, and so on.

[OO7]

As argi2007 stated in the opening post, the most significant performance gain from aerodynamics (down force) on a Formula 1 car is through cornering. I think this would be followed by braking and finally traction when accelerating. Because of this one would assume F1 teams spend a great deal of time focusing on aero with side-slip/yaw.

My question is, given a constant speed, do all F1 cars lose some down force while in yaw/side-slip when compared to the same speed in a straight line?

[Cold Fussion]

You will struggle to get representative CFD FSAE results in a straight line let alone complicating it with a yaw condition.

[mrluke]

As argi2007 stated in the opening post, the most significant performance gain from aerodynamics (down force) on a Formula 1 car is through cornering. I think this would be followed by braking and finally traction when accelerating. Because of this one would assume F1 teams spend a great deal of time focusing on aero with side-slip/yaw.

My question is, given a constant speed, do all F1 cars lose some down force while in yaw/side-slip when compared to the same speed in a straight line?

Some cars may give their optimum downforce under yaw..