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-   -   Turbulence Model and Meshing Advice (http://www.cfd-online.com/Forums/fluent/39456-turbulence-model-meshing-advice.html)

Jason January 31, 2006 10:18

Turbulence Model and Meshing Advice
 
I have a complex bluff body with cavities, gaps, and fins protruding from the body. I was asked to get the unsteady frequencies coming off these different features at compressible subsonic speeds (about Mach .5, and ignoring Fluid-Structure-Interaction, which we simply can't handle here).

I'm assuming this will get too complex for a realizable k-ep model, but can an RSM handle this, or do I have to go with an LES model? Also, as far as meshing goes, can I get away with using y+ values of around 30, or do I have to bring the mesh down to y+ value of around 1?

Any other advice is greatly appreciated as well.

Thanks, Jason

Razvan January 31, 2006 14:05

Re: Turbulence Model and Meshing Advice
 
I say that RSM will do the job respectably, even with y+=30, of course taking care to have a REAL B-L mesh (6-7 or better 10 layers, with lowest skewness possible), at least 2nd order discretisation and well resolved wakes. The only thing I'm worried about is the actual frequencies values you will obtain with RSM...

LES (or better DES in your case) will certainly do a much better job. One thing: computational effort with DES might be almost equal to a ordinary k-e unsteady calculation(I say this because I oftenly encountered this situation when doing my own calculations)!

Beware: DES comp. effort = k-e unsteady comp. effort means same CPU time for a time step! But that's it! The "problem" with DES is that you'll absolutely need more and sometimes smaller time steps to really converge the solution.

Anyway, if precision is what you're looking for, take DES. My advice.

Good luck, Razvan


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