[thintn222]

Hello all Foamers !

I'm doing a simulation evolved with bubble rising within a water domain at the moment. I met a serious problem about The Courant number keep bigger and bigger in each time step . Go with it is the max(magU) getting bigger and bigger too. I want to run the case at 200s time step and it diverged at around 2.5s .

I just use 90000 hexahedra number of cells , checkMesh is OK , i decrease the timestep even to 1e-10 it still diverged , i turned on the adjustableTimestep but it still had the same problem

One more thing I notice that the value of min(alpha1) suddenly decreased from 0 to -1e-9 . And when the value Max cell volume fraction is bigger than 1 with the min dense number of parces = 4 . It diverged immediately

Please help me out with this problem.! Below is my checkMesh log, fvSchemes and fvSolution and my boundary condition. Thanks so much for helping me!

checkMesh

Mesh stats
    points:           97061
    faces:            276900
    internal faces:   263100
    cells:            90000
    faces per cell:   6
    boundary patches: 3
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     90000
    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.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
    Patch               Faces    Points   Surface topology
    inlet               36       49       ok (non-closed singly connected)
    outlet              900      961      ok (non-closed singly connected)
    walls               12864    12936    ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (-0.075 -0.075 0) (0.075 0.075 0.5)
    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)
    Mesh has 3 solution (non-empty) directions (1 1 1)
    Boundary openness (-1.25066e-16 -1.31008e-17 1.48292e-18) OK.
    Max cell openness = 1.35525e-16 OK.
    Max aspect ratio = 1 OK.
    Minimum face area = 2.5e-05. Maximum face area = 2.5e-05.  Face area magnitudes OK.
    Min volume = 1.25e-07. Max volume = 1.25e-07.  Total volume = 0.01125.  Cell volumes OK.
    Mesh non-orthogonality Max: 0 average: 0
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 1.11023e-13 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

fvSolution:

solvers
{
    "alpha.water.*"
    {
        nAlphaCorr      2;
        nAlphaSubCycles 2;
        cAlpha          1;

        MULESCorr       yes;
        nLimiterIter    2;

        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-10;//1e-7;
        relTol          0;
        maxIter         100;
    }

    pcorr
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-10;//1e-5;
        relTol          0;
    }

    p_rgh
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-10;//1e-07;
        relTol          0.05;
    }

    p_rghFinal
    {
        $p_rgh;
        relTol          0;
    }

    "(U|k|epsilon).*"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-10;//1e-06;
        relTol          0;
    }

    kinematicCloud:alpha
    {
        solver          PCG;//GAMG;
        tolerance       1e-10;//1e-06;
        preconditioner  DIC;//
        relTol          0.01;
        smoother        GaussSeidel;
        cacheAgglomeration true;
        nCellsInCoarsestLevel 400;
        agglomerator    faceAreaPair;
        mergeLevels     1;
    }
}

PIMPLE
{
    momentumPredictor   no;//yes;//no;//yes;//no;
    nOuterCorrectors    2;
    nCorrectors         2;
    nNonOrthogonalCorrectors 1;
    pRefCell            0;
    pRefValue           0;

    residualControl
    {
       "(p|U|k|omega)"
       {
         tolerance 1e-4;
         relTol    0;
       }
    }
}

relaxationFactors
{
    equations
    {
       ".*"               0.5 ;
    }
}

fvSchemes:

ddtSchemes
{
    default         Euler;//backward;//Euler;//CrankNicolson 0.38;
}

gradSchemes
{
    default         Gauss linear;//cellLimited Gauss linear 1;
    //grad(U)         Gauss linear;//Gauss linear;
   // grad(p)         Gauss linear;//
}

divSchemes
{
    default         none;
    div(rhoPhi,U)               Gauss upwind;
    div(phi,alpha)              Gauss vanLeer01;//linear;//upwind;
    div(phirb,alpha)            Gauss linear;//interfaceCompression;//linear;
    div(alphaRhoPhic,k)         Gauss upwind;
    div(alphaRhoPhic,epsilon)   Gauss upwind;
    div((((alphac*rho)*nuEff)*dev2(T(grad(U))))) Gauss linear;
    div(phiGByA,kinematicCloud:alpha) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;//limited corrected 0.1;//uncorrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;//limited corrected 0.1;//corrected;
}

fluxRequired
{
    default         no;
    p_rgh;
    pcorr;
    alpha.water;
}

alpha.water.org

dimensions      [0 0 0 0 0 0 0];

internalField   uniform 1;

boundaryField
{
    inlet
    {
            type            zeroGradient;
    }
    outlet
    {
        type            inletOutlet;
        inletValue      uniform 0;
        value           uniform 0;
      }

    walls
    {
        type            zeroGradient;
    }
}

p_rgh

dimensions          [ 1 -1 -2 0 0 0 0 ];

internalField       uniform 0;

boundaryField
{
    inlet
    {
         type            fixedFluxPressure;
         value           uniform 0;
    }
    outlet
    {
        type            prghTotalPressure;
        p0              uniform 0;
        value           uniform 0;
    }
    walls
    {
        type            fixedFluxPressure;
        value           uniform 0;
    }
}

U

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    inlet
    {
        type               fixedValue;
        value              uniform (0 0 0);
    }
    outlet
    {
        type                 pressureInletOutletVelocity;
        value               $internalField;
        inletValue         $internalField;
    }
    walls
    {
          type                 fixedValue;
          value              uniform (0 0 0);
    }
}

[thintn222]

Update :

I quited control the value of Courant number , but another problem appeared.

The value of Phase-1 volume fraction keep increasing in each timestep and when it > 1 and min(alpha1) is negative . The simulation crashed again in ~6s

Any idea how to control this value !

Please help me, any advice are really appreciate !