[SeMar]

Hey guys,

I recently discovered, that some of my cases show checkerboarding in hanging nodes areas. This occurs visibly only in the temperature field.

My setup is roughly the following. First I solve the (laminar) impulse equation on the fluid domain with pimpleFoam while time averaging the velocity field. Then I copy the UMean to the main case and solve the energy equation on the multi domain (1 solid, 1 fluid) with chtMultiRegionFoam until the temperature on the outlet patch does not change.

I already tried different numerical schemes and switched to first order with no visible effect. The velocity field shows no oscillatory behaviour at all. Residuals are around 1e-5.
the fvSchemes files for the fluid domain is:

ddtSchemes
{
    default        backward;
}
gradSchemes
{
    default         cellMDLimited Gauss linear 0.5;
    grad(U)         cellMDLimited Gauss linear 0.5;
}
divSchemes
{
    default         none;
    div(((rho*nuEff)*dev2(T(grad(U)))))  Gauss linear;
    div(phi,U)      Gauss linearUpwind grad(U);
    div(phi,h)      Gauss linearUpwind default;
    div(phi,e)      Gauss linearUpwind default;
    div(phi,K)      Gauss linearUpwind default;
}
laplacianSchemes
{
    default         Gauss linear limited 0.777;
}
interpolationSchemes
{
    default         linear;
}
snGradSchemes
{
    default         limited 0.777;
}
fluxRequired
{
    default         no;
    p_rgh;
}

CheckMesh output is:

Overall domain bounding box (-0.0049 -0.0035 -0.0001) (0.0091 0.0035 0.0001)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (2.272174e-17 1.934456e-17 -5.833666e-17) OK.
    Max cell openness = 3.444354e-16 OK.
    Max aspect ratio = 6.548118 OK.
    Minimum face area = 2.401861e-12. Maximum face area = 1.000083e-08.  Face area magnitudes OK.
    Min volume = 4.095064e-18. Max volume = 1.000069e-12.  Total volume = 1.808073e-08.  Cell volumes OK.
    Mesh non-orthogonality Max: 58.54525 average: 7.599924
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 2.60591 OK.
    Coupled point location match (average 0) OK.
    Face tets OK.
    Min/max edge length = 2.005364e-07 0.000100008 OK.
   *There are 698 faces with concave angles between consecutive edges. Max concave angle = 43.46902 degrees.
  <<Writing 698 faces with concave angles to set concaveFaces
    Face flatness (1 = flat, 0 = butterfly) : min = 0.8599798  average = 0.9989744
    All face flatness OK.
    Cell determinant (wellposedness) : minimum: 0 average: 11.76043
 ***Cells with small determinant (< 0.001) found, number of cells: 4
  <<Writing 4 under-determined cells to set underdeterminedCells
 ***Concave cells (using face planes) found, number of cells: 25139
  <<Writing 25139 concave cells to set concaveCells
    Face interpolation weight : minimum: 0.1086233 average: 0.4817486
    Face interpolation weight check OK.
    Face volume ratio : minimum: 0.02250037 average: 0.9042536
    Face volume ratio check OK.

I attached a screenshot of the mesh, velocity- and temperature field, as well as the temperature log at the outlet.

Any comment is appreciated!