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Old   April 2, 2004, 04:16
Default symmetry is not symmetrical!
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Hi all

I have been simulating the flow of air over a symmetrical ship, and at 0 deg yaw (head-on to the wind) the flow should be symmetrical. It is not. I have tried many different meshes and adaptions, I have tried different turbulence models as well as inviscid flow, and I have re-scaled to reduce the Reynolds number. I cannot get a symmetrical flow. Any suggestions would be appreciated. Thanks.
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Old   April 2, 2004, 06:08
Default Re: symmetry is not symmetrical!
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first I'd like to ask, whether the solutions you got are well converged. It might just be that the solution slighly oscillates.

Secondly - the solution will not be completely symmetrical on unstructured non-symmetrical grid due to numerical errors. So you need to think about better mesh or perhaps solution-based adaption.

Third option is - if you know that the solution must be symmetrical on a physical basis, you may enforce such solution by simply generating grid for only a half of the symmetrical geometry.

Hope this helps George
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Old   April 2, 2004, 06:55
Default Re: symmetry is not symmetrical!
Dave Roper
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Thanks George

Yes the solutions are fully converged, I think the solution does oscillate slightly as a point velocity monitor shows this. The mesh is a combination of tet and hex cells, unstructured, and is not perfectly symmetrical. Solution adaptions have been done, but cannot achieve symmetry in the solution. I did wonder about the numerical errors. The solution is expected to be symmetrical and experimental validation has shown that it is, so I did think that a symmetry plane was my next move - just felt like cheating! Thanks for your help, Dave
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