[stuntmanmike]

Hi,

I am currently investigating the primary breakup of a liquid jet in a pressurized nitrogen atmosphere as preliminary investigations for my master thesis.
I am doing LES with interFoam in a simple cylindrical domain with an inlet diameter d. The domain extends over 15d in axial direction and 5d in radial direction (uniformly refined hexahedral with approx 10M cells).

physical parameters are:

d = 90e-6 m
v_liquid = 125 m/s
sigma = 0.0186 kg/s^2
rho_liquid / rho_gas = 24,19
Re = 16071
We = 51864
CFL = 0.1

The simulation and the breakup seem fine somehow (the mesh still is a bit too coarse to capture small droplets) but there are developing ripple-like instabilities on the mushroom shaped top of the jet which are clearly unphysical. I assumed they are caused by the mesh quality of the o-grid but after improving the mesh quality they still appear and I am running out of ideas how to fix this. I also read through some other threads and came accross the problem of parasitic currents caused by the CSF implementation. However they seems to be more a problem of surface tension dominated flows which is not the case here. Could this still be the problem?
I attached pics to show the problem. Does someone have an idea how to fix this??

Many thanks in advance
Simon

[akidess]

Case setup? What are you plotting?

[stuntmanmike]

The domain dimensions are as described. The liquid is entering the domain from a circular inlet in the center of the bottom plane of the cylinder and is flowing upwards. The plot is showing the interface alpha = 0.5. The mesh shows the bottom plane of the clinder (where the liquid enters in the center).

[akidess]

Solver and discretization settings not relevant?

[stuntmanmike]

Oh sorry.
The fvSchemes looks like that:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         Euler;
}

gradSchemes
{
    default         pointCellsLeastSquares; //Gauss linear;
}

divSchemes
{
    default             none;

    div(rhoPhi,U)      Gauss linearUpwind grad(U);
    div(phi,alpha)      Gauss vanLeer;
    div(phirb,alpha)    Gauss vanLeer;

    "div\(phi,(k|omega)\)"      Gauss upwind;
    div((muEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

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


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

I changed grad scheme from Gauss linear to pointCellsLeastSquares cause I read it gives more acurate results, however it didn't fix the problem.

The fvSolutions looks like that:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

        MULESCorr       yes;
        nLimiterIter    25;

        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-10;
        relTol          0;
    }

    pcorr
    {
        solver          PCG;
        preconditioner
        {
            preconditioner  GAMG;
            tolerance       1e-5;
            relTol          0;
            smoother        GaussSeidel;
            nPreSweeps      0;
            nPostSweeps     2;
            nFinestSweeps   2;
            cacheAgglomeration true;
            nCellsInCoarsestLevel 10;
            agglomerator    faceAreaPair;
            mergeLevels     1;
        }
        tolerance       1e-5;
        relTol          0;
        maxIter         100;
    }

    p_rgh
    {
        solver           GAMG;
        tolerance        5e-9;
        relTol           0.01;

        smoother         GaussSeidel;
        nPreSweeps       0;
        nPostSweeps      2;

        cacheAgglomeration true;

        nCellsInCoarsestLevel 10;
        agglomerator     faceAreaPair;
        mergeLevels      1;

        maxIter          100;
    };

    p_rghFinal
    {
        $p_rgh;
        tolerance       5e-9;
        relTol          0;
    }

    "(U|k|omega).*"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        nSweeps         1;
        tolerance       1e-6;
        relTol          0.1;
    };
}

PIMPLE
{
        momentumPredictor no;
        nCorrectors     2;
        nNonOrthogonalCorrectors 0;
    turbOnFinalIterOnly false;
    //nOuterCorrectors    25;
}

relaxationFactors
{
    fields
    {
    }
    equations
    {
        ".*" 1;
    }
}


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

I hope these are all relevant information.