Is that a checker-boarding pattern? How to avoid it?
 

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

I am trying with pisoFoam (transient solver) and results are not better.

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.