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-   -   turbulence modeling error at a stagnation point (http://www.cfd-online.com/Forums/cfx/22930-turbulence-modeling-error-stagnation-point.html)

erdem August 8, 2006 04:26

turbulence modeling error at a stagnation point
 
hi

I'm studying external aerodynamics of Ahmed Body car geometry. I have used realizable k-eps, SST k-omega and RSM models. in terms of drag coefficient I got similar values with all models. but all of them calculated nearly 1.5-2 times drag at the front of the body (comparing with the original experiments. Realizable k-epsilon has the highest drag on the front.

why does this happen? would you please help me about investigating the greater pressures at the front caused by turbulence modeling? I have to write a discussion about it. this is really important. thanks for you time.

Erdem

Glenn Horrocks August 8, 2006 22:48

Re: turbulence modeling error at a stagnation poin
 
Hi,

What do you mean by drag at the front of the body?

There is a validation case of the Ahmed body in the CFX-Community pages. I think you will find you will need LES/DES or SAS to get good drag results on the Ahmed body. It is a very challenging thing to get accurate results on.

Glenn Horrocks

IMAD August 9, 2006 02:04

Re: turbulence modeling error at a stagnation poin
 
I THINK YOU NEED TO REFIN MESH NEAR THE STAGNATION POINT WHERE VERY HIGH GRADIENT EXSIT

Glenn Horrocks August 9, 2006 19:54

Re: turbulence modeling error at a stagnation poin
 
Hi Imad,

It has been shown by many studies that a steady state assumption with RANS turbulence models of bluff body flows often leads to poor drag accuracy. There is only so far the extra grid refinement will go to improving accuracy if the fundamental physics are not being modelled correctly.

Glenn Horrocks


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