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wilson April 5, 2005 03:45

aerodynamic analysis
Hi guys

I am doing aerodynamic analysis of a small size car. Now I have put the car model in a rectangular box for simulation just like a wind tunnel testing experiment. But I am still uncertain about the distance between the wall of the tunnel and the car that should be kept in order to obtain no boundary effect of the wall. I read the documentation in which it is said to keep good distance between the wall and the car but nothing specific is mentioned. The wall boundary condition that I am setting is "free slip". if anyone can tell me a numerical ratio or a thumb rule for this problem.

regards wilson

Glenn Horrocks April 5, 2005 19:26

Re: aerodynamic analysis

Do a sensitivity analysis and work it out. I don't work in the field so I don't know a rule of thumb.

Glenn Horrocks

wilson April 6, 2005 03:45

Re: aerodynamic analysis
hi glenn can u elaborate on sensitivity analysis. if i am not wrong u mean to say that i increase or decrease the distance and check any effect occuring.

regards wilson

Akin April 6, 2005 05:40

Re: aerodynamic analysis
Look in the Ahmed body Model.

Michael Bo April 6, 2005 05:42

Re: aerodynamic analysis
Rule of thumb: Only up to 5% of the cross section area should be occupied by the car.

Glenn Horrocks April 6, 2005 18:34

Re: aerodynamic analysis
Hi Wilson,

That is correct. Even if you use a rule of thumb you should check the sensitivity for your model, so you know the level of accuracy you can expect from your model.

Glenn Horrocks

Marco Melo April 29, 2005 11:25

Re: aerodynamic analysis
Hi Wilson!

My Engineering thesis was the simulation of the FSAE car of my university, look you have to do like Micheal said. The cross section area of the car has to be 5-10 % of the cross section of the tunnel. I also put free slip for the upper surfaces and i put the bottom surface to move at the car speed. I'd like to know if you already have values of the aerodynamisc coefficient, so we can compare because we had problems with the magnitude.

Regards Wilson!

PS: my email adress is

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