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Is that a checker-boarding pattern? How to avoid it? |
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December 10, 2009, 06:02 |
Is that a checker-boarding pattern? How to avoid it?
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#1 |
Senior Member
Robert Castilla
Join Date: Apr 2009
Location: Spain
Posts: 109
Rep Power: 17 |
Hi,
I am simulating internal turbulent flow in complex geometries with simpleFoam and k-Omega SST, and I have found this strange behavior (see attached picture). The fvSolution and fvSchemes files are: solvers { p { solver GAMG; tolerance 1e-7; relTol 0.1; // preconditioner DIC smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; cacheAgglomeration on; agglomerator faceAreaPair; nCellsInCoarsestLevel 10; mergeLevels 1; }; U { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; }; k { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; }; omega { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; }; } SIMPLE { nNonOrthogonalCorrectors 0; } relaxationFactors { p 0.3; U 0.7; k 0.7; epsilon 0.7; } ----------------------------------------------------------------------- ddtSchemes { default steadyState; } gradSchemes { default Gauss linear; grad(p) Gauss linear; grad(U) Gauss linear; // grad(U) Gauss limitedLinear; } divSchemes { default none; div(phi,U) Gauss linearUpwindV cellLimited Gauss linear 1; div(phi,k) Gauss upwind; div(phi,omega) Gauss upwind; div((nuEff*dev(grad(U).T()))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; // default Gauss linear limited 0.5; // default Gauss linear limited 0.333; } interpolationSchemes { // default upwind phi; // interpolate(U) upwind phi; default linear; interpolation linear; } snGradSchemes { default corrected; } fluxRequired { default no; p; } ----------------------------------------------------------------------------------- I am not sure if it is the checker-boarding pattern. If it is, it should be avoided with SIMPLE, isn't it? Maybe have I to tune the SIMPLE parameters? Can somebody give me some hint? Thank you Robert |
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December 10, 2009, 08:45 |
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#2 |
Senior Member
Robert Castilla
Join Date: Apr 2009
Location: Spain
Posts: 109
Rep Power: 17 |
I am trying with pisoFoam (transient solver) and results are not better.
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December 11, 2009, 11:50 |
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#3 |
Senior Member
Robert Castilla
Join Date: Apr 2009
Location: Spain
Posts: 109
Rep Power: 17 |
It seems so be related to mesh. It has been meshed with snappyHexMesh. If there are sharp transitions of cell size, this kind of patterns arise. I don't know the reason, but I have tried with a regular (not grading) hexahedral mesh, it went fine. Maybe it is something that only happens when meshing with snappyHexMesh inan internal flow.
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