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Old   March 23, 2018, 18:42
Exclamation pimpleFoam blows up
  #1
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Hi guys,

I am running a simple case with pimpleFoam. I get way too high pressure gradient and velocity. The flow is laminar. My boundary conditions are:

Code:
dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{

    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value           uniform 0;
    }
    upperMembrane
    {
        type            zeroGradient;
    }
    lowerMembrane
    {
        type            zeroGradient;
    }
    spacers
    {
        type            zeroGradient;
    }
    so1
    {
    type        zeroGradient;
    }
    so2
    {
    type        zeroGradient;
    }


}

Code:
internalField   uniform (0.1 0 0);

boundaryField
{

    inlet
    {
        type            fixedValue;
        value           uniform (0.1 0 0);
    }
    outlet
    {
        type            zeroGradient;
    }
    upperMembrane
    {
    type            fixedValue;
        value           uniform (0 0 0);
    }
    lowerMembrane
    {
    type            fixedValue;
        value           uniform (0 0 0);
    }
    spacers
    {
    type            fixedValue;
        value           uniform (0 0 0);
    }
    so1
    {
    type            fixedValue;
        value           uniform (0 0 0);
    }
    so2
    {
    type            fixedValue;
        value           uniform (0 0 0);
    }
}

And my checkMesh looks like this:
Code:
Mesh stats
    points:           2969007
    faces:            30898219
    internal faces:   29458877
    cells:            15089274
    faces per cell:   4
    boundary patches: 7
    point zones:      0
    face zones:       1
    cell zones:       1

Overall number of cells of each type:
    hexahedra:     0
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    15089274
    polyhedra:     0

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
    Patch               Faces    Points   Surface topology                  
    inlet               47683    24840    ok (non-closed singly connected)  
    lowerMembrane       439090   221519   ok (non-closed singly connected)  
    outlet              47664    24830    ok (non-closed singly connected)  
    so1                 47666    24833    ok (non-closed singly connected)  
    so2                 47727    24869    ok (non-closed singly connected)  
    spacers             370831   189841   ok (non-closed singly connected)  
    upperMembrane       438681   221236   ok (non-closed singly connected)  

Checking geometry...
    Overall domain bounding box (3.5e-05 3.5e-05 -2.273737e-13) (0.00446501 0.004465 0.001)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-1.761814e-15 -3.603008e-16 -2.208104e-13) OK.
    Max cell openness = 3.941394e-16 OK.
    Max aspect ratio = 18.79829 OK.
    Minimum face area = 1.058019e-12. Maximum face area = 2.042148e-09.  Face area magnitudes OK.
    Min volume = 1.351823e-18. Max volume = 3.658189e-14.  Total volume = 1.819464e-08.  Cell volumes OK.
    Mesh non-orthogonality Max: 78.37398 average: 11.61264
   *Number of severely non-orthogonal (> 70 degrees) faces: 1584.
    Non-orthogonality check OK.
  <<Writing 1584 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
    Max skewness = 1.393563 OK.
    Coupled point location match (average 0) OK.

Mesh OK.
And my fvSolution looks like

Code:
solvers
{
    p
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.01;
    //Iter          20;

        smoother         DICGaussSeidel;

    }

    pFinal
    {
        $p;
        relTol          0;
    }

    "(U|k|epsilon)"
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance       1e-05;
        relTol          0.1;
    }

    "(U|k|epsilon)Final"
    {
        $U;
        relTol          0;
    }
}
I am thinking the reason for the blow-up is because the existence of the large amount of non-orthogonal mesh (as I highlighted in red). But I am not sure if this is the only reason leading to the blow-up. Is there any other possible reason for this blow-up?

Thx.
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Old   March 24, 2018, 01:08
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Uwe Pilz
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What you show from your case looks good.

I recommend to set the initial field velocity to 0, write the results at every time step and look what happens. If the instability arises from the region where the mesh is unfavorable you have it.
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