[Werne]

Hello,

I'm trying to simulate the flow between an inner rotating cone and an outer stationary cone for my master thesis. My Geometry is a small "wedge" of 7.5° with cyclicAMI-boundary conditions at both sides.

I use a totalPressure condition at the inlet and a massflow outlet condition.

In the picture below you cann see, that the residuals start rising again after a few hundred iterations, and that they start oscillating after a few thousand iterations. And finally, a few hours after the osciallations started the simulation chrashes.

The little "peaks" after 1000 iteratins originate from a change in the boundary conditions: In order to get a stable simulation I have to start with a pressure driven flow. Only after the flow has settled I can switch to the massflow boundary condition.

My boundary conditions:

Pressure-field:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.2                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 362900;

boundaryField
{
    INLET
    {
    type            totalPressure;
    gamma 1.4;
    p0 uniform 362900; // total pressure 362900
    value uniform 362900; 
    }

    OUTLET
    {
        type            zeroGradient;
    }

    SYM_1_OBEN
    {
        type            cyclicAMI;
    }

    SYM_1_UNTEN
    {
        type            cyclicAMI;
    }

    SYM_2_OBEN
    {
        type            cyclicAMI;
    }

    SYM_2_UNTEN
    {
        type            cyclicAMI;
    }

    MOVINGWALL_OBEN
    {
        type            zeroGradient;
    }

    MOVINGWALL_UNTEN
    {
        type            zeroGradient;
    }

    BOHRUNG
    {
        type            zeroGradient;
    }

    WALL_OBEN
    {
        type            zeroGradient;
    }

    WALL_UNTEN
    {
        type            zeroGradient;
    }

    PLENUMWALL
    {
        type            zeroGradient;
    }

    KEIL
    {
        type            zeroGradient;
    }

    GAP_S
    {
        type            zeroGradient;
    }

    GAB_W
    {
        type            zeroGradient;
    }
}
// ************************************************************************* //

Velocity-field:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.2                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0);

boundaryField
{
    INLET
    {
        type            zeroGradient;
    }

    OUTLET
    {
        type            flowRateInletVelocity;
        massFlowRate    constant -0.003833;    //-0.004167
        value           uniform (0 0 0);
    }

   SYM_1_OBEN
    {
        type            cyclicAMI;
    }

    SYM_1_UNTEN
    {
        type            cyclicAMI;
    }

    SYM_2_OBEN
    {
        type            cyclicAMI;
    }

    SYM_2_UNTEN
    {
        type            cyclicAMI;
    }

    MOVINGWALL_OBEN
    {
        type            rotatingWallVelocity;
    origin        (0 0 0);
    axis        (1 0 0);
    omega        838;
    }

    MOVINGWALL_UNTEN
    {
        type            rotatingWallVelocity;
    origin        (0 0 0);
    axis        (1 0 0);
    omega        838;
    }

    BOHRUNG
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    WALL_OBEN
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    WALL_UNTEN
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    PLENUMWALL
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    KEIL
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    GAP_S
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    GAB_W
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

}

// ************************************************************************* //

fvSchemes:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.2                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         steadyState;
}

gradSchemes
{
    default         cellLimited Gauss linear 1.0;
}

divSchemes
{
    default    bounded Gauss upwind;
    div(phi,U)      bounded Gauss upwind;//bounded Gauss upwind;
    div((muEff*dev2(T(grad(U))))) Gauss linear;
    div(phi,e)      bounded Gauss upwind;
    div(phi,k)      bounded Gauss linear;
    div(phi,omega)      bounded Gauss linear;
    div(phi,Ekp)    bounded Gauss upwind;
}

laplacianSchemes
{
    default      Gauss linear limited 0.5; //Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         limited 0.5; //corrected
}

fluxRequired
{
    default         no;
    p               ;
}


// ************************************************************************* //

fvSolution:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.2                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver          GAMG;
        tolerance       1e-08;
        relTol          0.05;
        smoother        GaussSeidel;
        cacheAgglomeration off;
        nCellsInCoarsestLevel 20;
        agglomerator    faceAreaPair;
        mergeLevels     1;
    }

    U
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        nSweeps         2;
        tolerance       1e-08;
        relTol          0.1;
    }  

    e
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-15;   //1e-09
        relTol          0.1;
    }

    "(k|omega)" 
    {
        $U;
        tolerance       1e-09;
        relTol          0.1;
    }    
 
}

SIMPLE
{
    nNonOrthogonalCorrectors 2;
    rhoMin          rhoMin [ 1 -3 0 0 0 ] 1.5;
    rhoMax          rhoMax [ 1 -3 0 0 0 ] 5;
   // transonic    true;

    residualControl
    {
        p               1e-6;        
        U               1e-6;        
        e               1e-6;        

        // possibly check turbulence fields
           "(k|epsilon|omega)" 1e-9;    
    }
}

relaxationFactors
{
    fields
    {
        p               0.3; //0.1
        rho             0.05; //0.05
    }
    equations
    {
        U               0.7; //0.7
        k        0.7; //0.7
        omega        0.7; //0.7
        e               0.3; //0.7
    }
}

potentialFlow
{
    nNonOrthogonalCorrectors 10;
}


// ************************************************************************* //

What could be the cause for the rising residuals?
Could it be, that the "flowrateInletVelocity" causes those problems?

I considered using a pressure condition for the outlet as well, but the problem with this approach is, that the fluid at the outlet has a very high rotational velocity so that there is a large pressure variation over the diameter.