[vinz]

Hi everybody,

I'm interested in automotive (more specificaly racing car) simulation. I'd like to know if someone allready tried to simulate such things using OpenFOAM.
Furthermore, a lot of test cases can be found on wings simulation for instance, does someone know if similar test cases can be found for cars?
Any informations are welcome.

Vincent

[bastil]

Hi Vincent,

I think this is a interesting topic. What racing cars are you exactly interested in? I also considered that but I have not found any caeses.

Basti

What exactly are you trying to simulate? Engine combustion, Aerodynamic drag, down force, etc.. ?

It sounds as if your trying to do aerodynamics of some sort.

I'm trying to learn openfoam and CFD myself. As my first exercise I was going to see what sort of drag my Mercedes 300SD had at mach 2.5. I will try and come up with a tutorial as I learn how to do it. It may take a while though as I'm quite busy and trapped using windows until I get some work projects done.

[vinz]

Hi all,

Indeed, I'd like to do aerodynamics (drag,...) on a racing car. I would like to try a formula 1 or something like that (something quite fast).
I'm facing another problem, the need of some interesting stl files to mesh. Does someone know a kind of data bank of stl files?
Thanks for the answers.

Vincent

I use blender ( http://www.blender.org/ ) to convert common file types to stl files. That is how I got the data for my car.

[vinz]

Hi Conn Clark,

I allready use blender to convert files to stl. The problem is to obtain original files.
What was the original extension of your car? 3ds?iges? step?
Are there data banks of any of these formats?
Thanks for your help.

Vincent

look here for some free car models http://dmi.chez-alice.fr/models1.html

There is a links section that has a list of sites that have free models.

Just remember your going to need a lot of compute time to simulate for these.

[bastil]

HI,

also remember that for these complex geometris mesh generation is a challange. I guess you need some commercial meshers. What program are you thinking about?

Basti

[vinz]

Hi,

Thanks for the link. It's very usefull.

For the mesher, I'll use the one we use usually, i.e GridPro.

And I'd like to try, two cfd codes OpenFOAM, and our in-house developed code named MISTRAL.

Vincent

[seang]

try the Ahmed bluff body. relatively simple geometry, but plenty of measurements available.

[vinz]

Hi Kuan,

Thanks for the hint. Indeed I found some papers on the topic. I'll do the mesh today and will begin the simulations after.

I'll inform everydody of my results when available.

Vincent

[vega]

Vincent,
A very good reference for Automotive Aerodyanmics is:
Aerodynamics of Road Vehicles, by W. Hucho

[vinz]

Thanks,
I order it on amazon right now.

The mesh for the ahmed bluff body is allmost ready and I should be able to get some results next week.

Vincent

[vinz]

Hi everybody,

First of all thanks Rajneesh for the advise on the book, I received it and it's great.

However I need some help to run the ahmed test case on openfoam. I tried to use simpleFoam but I don't get the results I want.

Do you people think simpleFoam is the right solver to use in this case? Are there other more suited solvers available in OpenFOAM for this kind of studies?

Thanks in advance for your help.

Vincent

[cedric_duprat]

Hi Vincent,

what do you mean by "I don't get the results I want" cause this is exactly the good question...
what do you want ?
simpleFoam is a RANS, steady solver so, if you are looking for unsteady turbulent structure, simpleFoam won't be the best way.
I know that some teams are working on a coupled RANS/LES for this test case so :
1- only LES is not possible yet
2- RANS may be not enought.

Well, nice speatch, ...
hope it can help you

regards,
Cedric

[vinz]

Hi Cedric,

I saw this problem regarding RANS and LES.
Looks like the RANS/LES approach is the best way to do it but I guess such approach being experimental so far, it's not implemented in OpenFOAM.

Actually when I say "I don't get the good results", I'm closer to a "I don't get results at all!!!". In fact running with simpleFoam is ok if I don't use a refined mesh at the wall which I don't like that much because of poor boundary layer catching.

Then if I used a refined boundary layer (around 1e-05 for the first cell thick) the computation is crashing after few iterations...which is even worse than the first approach.

To be simple my goal is to simulate a racing car! To do that, I'd like to validate the code before on simpler cases, and the ahmed one looks a good choice. Then the question is:
In your opinion (cedric or others), what is the best solvers for this kind of case in OpenFOAM? Or is it totaly impossible to do race cars simulations using OpenFOAM (that's not a blame, just a question)?

I hope I've been more clear. Thans for your help.

Vincent

[fra76]

Sometimes problems like this are related to the turbulence model.
Try to run the simulation for a few iterations without turbulence, and then switch it on.
Or use small underrelaxation factors for a while.
Or use a different turbulence model (relizable key-epsilon, RNG key-epsilon, kOmegaSST, ...)
Or any combinations of the above!

A couple of years ago, one of my students produced some very nice results on a Ahmed body...

[vinz]

Hi Francesco,

Nice to know that somebody succeed. There is some hope!

Actually for my simulation, even running without turbulence doesn't solve the problem.

I would be interested to know which solver your student used (environment and boundary conditions..etc). Do you have a paper with its results maybe? It could help me to find my problem, at least to make it run, we'll see look for result accuracy later!

Anyway thanks for the reply.

Vincent

[ariorus]

Just out of curiosity: what is the Reynolds number in the test you mentioned? What kind of turbulence model are you using in simpleFoam?

[vinz]

Hi Rosario,

nu is equal to 1.475e-05, U=60m/s and the length of the body is 1.044m. So I would say the Reynolds number is around 4.24678e06.
But I tried something much smaller by using nu of 0.1 and it doesn't change anything.
I may post the case this afternoon. It will give the possibility to other people to have a look at the settings.

Vincent