[klitz]

Hi everyone,

I am trying to simulate a NASA validation case in OpenFOAM. Link to case https://www.grc.nasa.gov/WWW/wind/valid/arn/index.html. I'm using the given 2D grid in the link. Boundary conditions are also given. My problem is that I can't reach convergence with or without turbulence on especially in pressure. I am using simpleFoam. Should I use compressible solvers or change some of the boundary conditions? Because I am not sure about the arbitrary flow(inflow in case dic) should be zeroGradient or not(in U). And since I dont know the inlet velocity how can I find k and omega(below i used 0.01 Mach to calculate k and exit diameter of the nozzle for turbulence lenght scale to calculate omega) ? Also, for turbulence BC's at wall should I use 1e-10(I have seen some threads not to use 0) or the values I find for the inlet? Below you can find the case directories:

Pressure

internalField   uniform 98588.02;

boundaryField
{
    inflow
    {
        type            totalPressure;
        p0              uniform 183483.281;
    }

    outflow
    {
        type            totalPressure;
        p0           uniform 98595.03;
    }

    Freestream
    {
        type            totalPressure;
        p0           uniform 98595.03;
    }

    v_wall
    {
        type            zeroGradient;
    }

    i_wall
    {
        type            zeroGradient;
    }

    BaseAndTop
    {
        type            empty;
    }
}

Velocity

internalField   uniform (3.48 0 0);


boundaryField
{
    Freestream
    {
        type            inletOutlet;
        inletValue      uniform (3.48 0 0);
        value           uniform (3.48 0 0);
    }

    inflow
    {
        type            zeroGradient;
    }

    outflow
    {
        type            inletOutlet;
        inletValue      uniform (3.48 0 0);
        value           uniform (3.48 0 0);
    }

    i_wall
    {
        type            slip;
    }

    v_wall
    {
        type            noSlip;
    }

    BaseAndTop
    {
        type            empty;
    }
}

omega

internalField   uniform 8.2883133;

boundaryField
{
    inflow
    {
        type            fixedValue;
        value           $internalField;
    }
    Freestream
    {
        type            fixedValue;
        value           $internalField;
    }
    outflow
    {
        type            zeroGradient;
    }
    i_wall
    {
        type            omegaWallFunction;
        value           uniform 8.2883133;
    }
    v_wall
    {
        type            omegaWallFunction;
        value           uniform 8.2883133;
    }
    BaseAndTop
    {
        type            empty;
    }
}

k

internalField   uniform 0.04432;

boundaryField
{
    inflow
    {
        type            fixedValue;
        value           uniform 0.04432;
    }
    Freestream
    {
        type            zeroGradient;
    }
    outflow
    {
        type            zeroGradient;
    }
    i_wall
    {
        type            kqRWallFunction;
        value           uniform 1e-10;
    }
    v_wall
    {
        type            kqRWallFunction;
        value           uniform 1e-10;
    }
    BaseAndTop
    {
        type            empty;
    }
}

and also checkMesh -allTopology -allGeometry

Mesh stats
    points:           119642
    internal points:  0
    edges:            297861
    internal edges:   58581
    internal edges using one boundary point:   0
    internal edges using two boundary points:  58581
    faces:            237420
    internal faces:   117780
    cells:            59200
    faces per cell:   6
    boundary patches: 6
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     59200
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     0

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Topological cell zip-up check OK.
    Face-face connectivity OK.
  <<Writing 6 cells with two non-boundary faces to set twoInternalFacesCells
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
    Patch               Faces    Points   Surface topology                   Bounding box
    Freestream          320      642      ok (non-closed singly connected)   (-0.644917 4.16667 0) (6.66667 4.16667 0.0223293)
    i_wall              360      722      ok (non-closed singly connected)   (-0.644917 0 0) (6.66667 0 0.0223293)
    inflow              160      324      ok (non-closed singly connected)   (-0.645 0 0) (-0.644917 4.16667 0.0223293)
    outflow             180      362      ok (non-closed singly connected)   (6.66667 0 0) (6.66667 4.16667 0.0223293)
    v_wall              220      442      ok (non-closed singly connected)   (-0.645 0.08333 0) (0 0.354167 0.0223293)
    BaseAndTop          118400   119642   ok (non-closed singly connected)   (-0.645 0 0) (6.66667 4.16667 0.0223293)

Checking geometry...
    Overall domain bounding box (-0.645 0 0) (6.66667 4.16667 0.0223293)
    Mesh has 2 geometric (non-empty/wedge) directions (1 1 0)
    Mesh has 2 solution (non-empty) directions (1 1 0)
    All edges aligned with or perpendicular to non-empty directions.
    Boundary openness (-6.86038e-19 1.70069e-18 9.86545e-16) OK.
 ***High aspect ratio cells found, Max aspect ratio: 1008.9, number of cells 3
  <<Writing 3 cells with high aspect ratio to set highAspectRatioCells
    Minimum face area = 6.86882e-09. Maximum face area = 0.0691225.  Face area magnitudes OK.
    Min volume = 1.53376e-10. Max volume = 0.00154346.  Total volume = 0.679026.  Cell volumes OK.
    Mesh non-orthogonality Max: 70.7303 average: 9.90224
   *Number of severely non-orthogonal (> 70 degrees) faces: 1.
    Non-orthogonality check OK.
  <<Writing 1 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
    Max skewness = 0.780396 OK.
    Coupled point location match (average 0) OK.
    Face tets OK.
   *Edges too small, min/max edge length = 6.86878e-06 0.450016, number too small: 406
  <<Writing 406 points on short edges to set shortEdges
    All angles in faces OK.
    Face flatness (1 = flat, 0 = butterfly) : min = 1  average = 1
    All face flatness OK.
    Cell determinant (wellposedness) : minimum: 1.39417e-05 average: 1.14028
 ***Cells with small determinant (< 0.001) found, number of cells: 1223
  <<Writing 1223 under-determined cells to set underdeterminedCells
    Concave cell check OK.
    Face interpolation weight : minimum: 0.411365 average: 0.487032
    Face interpolation weight check OK.
    Face volume ratio : minimum: 0.69873 average: 0.947747
    Face volume ratio check OK.

Failed 2 mesh checks.

End

fvSolution

solvers
{
    p
    {
        solver          PCG;
        tolerance       1e-10;
        preconditioner  FDIC;
        relTol          0.1;
        smoother        GaussSeidel;
    }

    "(U|k|omega|nut)"
    {
        solver          PBiCG;
        smoother        symGaussSeidel;
        preconditioner  DILU;
        tolerance       1e-10;
        relTol          0.1;
    }
}

SIMPLE
{
    nNonOrthogonalCorrectors 2;
    consistent      yes;

    residualControl
    {
        p               1e-6;
        U               1e-6;
        "(k|omega|nut)" 1e-4;
    }
}

relaxationFactors
{
    equations
    {
        U               0.45; 
        omega           0.3;
        nut             0.3;
        k               0.3;
        p               0.25;
    }
}

fvSchemes

ddtSchemes
{
    default         steadyState;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         Gauss linear;
    div(phi,U)      Gauss limitedLinearV 1;
    div(phi,k)      Gauss upwind;
    div(phi,omega)  Gauss upwind;
    div((nuEff*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

wallDist
{
    method meshWave;
}

I know it says 2 mesh checks failed but since they were able to obtain convergent solution I thought I would be able to get a convergent solution also. Dimensions of the nozzle is given in the attachments. Any recommendation would be appriciated.

Thank you.

[dlahaye]

Definitely use compressible solver like e.g. rhoSimple. Possibly try some tutorials first. Make sure that checkMesh gives no errors.

[klitz]

OK thank you, I will try compressible solver. I also tried with a mesh which did not help with the issues. Would you please comment on the BC's? To me U and p look appropriate for this simulation however, I am not sure about the omega and k BC's since I am not sure about which dimension to use for turbulent length scale.

[dlahaye]

Chapter 16 of 2. Moukalled, Manga and Darwish, The finite volume method in computational fluid dynamics, Springer 2015 , http://www.springer.com/gp/book/9783319168739

[klitz]

Originally Posted by dlahaye

Chapter 16 of 2. Moukalled, Manga and Darwish, The finite volume method in computational fluid dynamics, Springer 2015 , http://www.springer.com/gp/book/9783319168739

Thank you I will check the chapter.