[Gesetzt]

I'm simulating the flow in a capillary with a sudden expansion with OF 2.4.0. The small capillary has a diamater of 250 µm. The big capillar has a diamater of 1000 µm. My flow rate ist $ 1\frac{ml}{min} $. Using standard properties of water I have a Reynolds number of 85 in my small pipe. For my mesh I choose one similar to this case: https://openfoamwiki.net/index.php/S...rupt_Expansion. I am using a low-Re mesh. I simulated it laminar first, but it seems unphysical to me, because I couldn't see any vortex, but because of the high expansion ratio one would expect a vortex after the sudden diameter change.

Now I'm using k-omega-SST and get a vortex, but after the expansion the flow isn't going back to a full developed profile.( I had the same issue with laminar simulation) I tried to make the second part of my geometry longer, but it doesn't effect the result. What seems strange to me:

GAMG: Solving for p, Initial residual = 0.00667948, Final residual = 6.67903e-06, No Iterations 927
time step continuity errors : sum local = 8.36257e-10, global = 2.7631e-10, cumulative = -0.00370942

First I need a lot of iterations for pressure and second only the cumulative error is much higher than the others. Also have to say, that it doesn't really change much with more iterations.

I attached some pictures of the solution below. Line plots are through the centerline.

Right now I'm really stuck and don't have any ideas what to change.

Here are my boundary conditions:

k:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.5                                   |
|   \\  /    A nd           | Web:      http://www.OpenFOAM.org               |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      k;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 3.65e-04;

boundaryField
{
    inlet           
    {
        type            fixedValue;
        value           uniform 3.65e-04;
    }

    outlet          
    {
        type            zeroGradient;
    }

    /*walls
    {
        type            fixedValue;
        value           uniform 1e-11;
    }
*/
walls
    {
       type            kqRWallFunction;
       value           uniform 1e-11;
    }

}

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

omega:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.5                                   |
|   \\  /    A nd           | Web:      http://www.openfoam.org               |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version 2.0;
    format ascii;
    class volScalarField;
    object omega;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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


internalField   uniform 5000.15;

boundaryField
{
    inlet
    {
        type            fixedValue;
        value           uniform 5000.15;
    }

    outlet
    {
        type            zeroGradient;
    }

    walls
    {
        //type            fixedValue;
        //value           uniform 1e-11;
        type omegaWallFunction;
        value uniform 1e-11;
    }

}

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

p:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }

    outlet
    {
        type            fixedValue;
        value           uniform 0;
    }

    walls
    {
        type            zeroGradient;
    }
}

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

U:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    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                flowRateInletVelocity;
        volumetricFlowRate  1.6646690e-08;
        value uniform       (0 0 0); 
    }
    */

 inlet
    {
        type                groovyBC;
        value               uniform  (0 0 0);
        variables 
            (

                "profile= ( - 1*6.78e-01 / pow(max(pts().x),2) * (pow(pos().y,2) + pow(pos().x,2)) + 1*6.78e-01);"
            );
        valueExpression "-normal()*profile";
    }


/*inlet
    {
        type                fixedValue;
        value               uniform  (0 0 0.001);
    }
    */

    outlet
    {
        type            zeroGradient;
    }

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

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

Here is also my fvSolution:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
// Ziel: Cumulative Error Roundabout 1e-08 zum Schluss!
solvers
{
    p
    {
        solver          GAMG;
        tolerance       1e-06; // 1.)1e-04 2.) 1e-05 3.)1e-06 4.) 1e-07
        relTol          0.01; //1.)0.2, 2.)0.01
        smoother        GaussSeidel;
        nPreSweeps      1;//1
        nPostSweeps     2;
        cacheAgglomeration on;
        agglomerator    faceAreaPair;
        nCellsInCoarsestLevel 10; // 10
        mergeLevels     1;
        maxIter         1000; 
    }

    "(U|k|epsilon|R|nuTilda|omega)"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-06; // 3.) 1e-06 4.) 1e-07
        relTol          0.1; // 0.1
    }
}

SIMPLE
{
    nNonOrthogonalCorrectors 0; //1

    residualControl
    {
        p               1e-3;
        U               1e-3;
        "(k|epsilon|omega)" 1e-3;
    }
}

relaxationFactors
{
    fields
    {
        p               0.5; //1).0.62.)3.)0.4
    }
    equations
    {
        U               0.7;
        k               0.7;
        epsilon         0.7;
        R               0.7;
        nuTilda         0.7;
    }
}


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

My fvSchemes:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    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         Gauss linear;
}

divSchemes
{
    default         none;
    div(phi,U)      bounded Gauss upwind;
    div(phi,nuTilda) bounded Gauss upwind;
    div(phi,omega) bounded Gauss upwind;
    div(phi,k) bounded Gauss upwind;
    div(phi,epsilon) bounded Gauss upwind;
    div((nuEff*dev(T(grad(U))))) Gauss linear;
    div((nuEff*dev2(T(grad(U))))) Gauss linear;

}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p               ;
}


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

Best Regards,
Gesetzt