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turbulence modeling error at a stagnation point

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Old   August 8, 2006, 04:26
Default turbulence modeling error at a stagnation point
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erdem
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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
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Old   August 8, 2006, 08:47
Default Re: turbulence modeling error at a stagnation poin
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Jonas Larsson
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The RSM model should not produce too high total pressures in the leading edge region, assuming that you have used it correctly and are not using a near-wall model which does have the leading edge problem that you refer to. The SST and Realizable models might give a bit too high total pressures in the leading edge region. Although these models are much less common to create this problem than for example the standard k-epsilon model.

Have you tried to use different grids and change the extent of your region? To obtain representative drag forces you often need to use a validated type of mesh. It should be extended far away upstream and any side-wall effects must be small.
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Old   August 8, 2006, 10:28
Default Re: turbulence modeling error at a stagnation poin
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erdem
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thank you for your help Lars but I wonder if I can find further info aboue these models. do you have a reference paper or something about the properties of these turbulence models?

thanks

erdem

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