[Phil_]

Hi all,

I’m working on an incompressible swirling flow through a nozzle and diffuser (Re=30.000) using simpleFoam and OF 2.3.0.

For swirling flows I read it’s best to use at least a non-linear k-epsilon turbulence model. Therefore I tried using the NonlinearKEShih model, but I’m running into problems with bounding epsilon and large continuity errors.

Usually the mesh is responsible for such behavior, so I tried simulating with different meshes (I attached one example with 300.000 hex cells). CheckMesh says:

Checking geometry...
    Overall domain bounding box (-0.01 -0.01 0) (0.01 0.01 0.08)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (2.2471e-16 3.30698e-16 9.79651e-16) OK.
    Max cell openness = 3.20034e-16 OK.
    Max aspect ratio = 7.45964 OK.
    Minimum face area = 1.015e-08. Maximum face area = 7.58503e-07.  Face area magnitudes OK.
    Min volume = 4.07554e-12. Max volume = 2.01323e-10.  Total volume = 1.07521e-05.  Cell volumes OK.
    Mesh non-orthogonality Max: 27.1515 average: 7.1929
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.883193 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

Boundary Conditions:
For the velocity inlet I use the profile1DfixedValue to define the axial and tangential components (http://openfoamwiki.net/index.php/Si...le1DfixedValue), fixedValue 0 at the walls, and zeroGradient at the outlet.

For pressure I use zeroGradient at the inlet and walls, and fixedValue 0 at the outlet.

For k and epsilon I estimated inlet values (k fixedValue 0.0035, epsilon fixedValue 0.0183). At the walls I usually used kqRWallFunction and epsilonWallFunction but checkPatchFieldTypes forced me to use a zeroGradient-condition. Does anyone know how the wall functions work in the Shih-model? The mesh has to be a High-Re-Mesh with y+>30, am I right? Also zeroGradient at the outlet for k and epsilon.

I experimented with different fvSolution and fvScheme adjustments. Here are the current ones:

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default steadyState;
}

gradSchemes
{
    default         Gauss linear;
    grad(p)         Gauss linear;
    grad(U)         Gauss linear;
}

divSchemes
{
    default         none;
    div(phi,U)      bounded Gauss linearUpwind Gauss;
    div(phi,k)      bounded Gauss upwind;
    div(phi,epsilon) bounded Gauss upwind;
    div(phi,R)      Gauss upwind;
    div(R)          Gauss linear;
    div(phi,nuTilda) Gauss upwind;
    div((nuEff*dev(T(grad(U))))) Gauss linear;
    div(nonlinearStress) Gauss linear;
}

laplacianSchemes
{
    default         none;
    laplacian(nuEff,U) Gauss linear corrected;
    laplacian((1|A(U)),p) Gauss linear corrected;
    laplacian(DkEff,k) Gauss linear corrected;
    laplacian(DepsilonEff,epsilon) Gauss linear corrected;
    laplacian(DREff,R) Gauss linear corrected;
    laplacian(DnuTildaEff,nuTilda) Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
    interpolate(U)  linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p;
}

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
  solvers
{
    p
    {
        solver           GAMG;
        tolerance        1e-5;
        relTol           0.01;
        smoother         GaussSeidel;
        nPreSweeps       0;
        nPostSweeps      2;
        cacheAgglomeration on;
        agglomerator     faceAreaPair;
        nCellsInCoarsestLevel 450;
        mergeLevels      1;
    }
 
      "(U|k|epsilon|R|nuTilda)"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-8;
        relTol          0.0;
    }
}


SIMPLE
{
    nNonOrthogonalCorrectors 0;
    pRefCell                 0;
    pRefValue                0;
}

relaxationFactors
{
    p               0.3; 
    U               0.7; 
    k               0.5; 
    epsilon         0.5; 
    R               0.7;
    nuTilda         0.7;
}

Any suggestions?

Thanks & regards,

Philip