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Weird results in MRF simulation of stirred tank with a steady state k-w SST model

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Old   January 2, 2015, 16:05
Default Weird results in MRF simulation of stirred tank with a steady state k-w SST model
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amine
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Location: FRANCE
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Dear,

I need your help to understand why I have no logical physical result of velocity and pressure.

I have done an MRF simulation of stirred tank with a steady state k-w SST model

rotational velocity 100 rpm

Material : water

fvSolution
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version 2.0;
    format ascii;
    class dictionary;
    location system;
    object fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
    SIMPLE
    {
        nNonOrthogonalCorrectors 0;
        pressureImplicitPorousity false;
        pRefCell 0;
        pRefValue 0;
        residualControl
        {
            U 1.0E-5;
            k 1.0E-5;
            epsilon 1e-5;
            omega 1.0E-5;
            nuTilda 1e-5;
            T 1e-5;
            p_rgh 1e-5;
            p 1.0E-5;
        }

    }

solvers
{
    p
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.01;
        smoother         GaussSeidel;
        nPreSweeps       0;
        nPostSweeps      2;
        cacheAgglomeration on;
        agglomerator     faceAreaPair;
        nCellsInCoarsestLevel 10;
        mergeLevels      1;
    }

    U
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.1;
        nSweeps          1;
    }

    k
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.1;
        nSweeps          1;
    }

    omega
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.1;
        nSweeps          1;
    }
}

potentialFlow
{
    nNonOrthogonalCorrectors 10;
}

relaxationFactors
{
    fields
    {
        p               0.3;
    }
    equations
    {
        U               0.7;
        k               0.7;
        omega           0.7;
    }
}

cache
{
    grad(U);
}
// ************************************************************************* //
fvSchemes

Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         steadyState;
}

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

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

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p;
}

// ************************************************************************* //
controlDict
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version 2.0;
    format ascii;
    class dictionary;
    location system;
    object controlDict;
}

    startFrom startTime;
    startTime 0;
    stopAt endTime;
    endTime 1000;
    deltaT 1;
    writeControl timeStep;
    writeInterval 100;
    purgeWrite 0;
    writeFormat ascii;
    writePrecision 10;
    writeCompression uncompressed;
    timeFormat general;
    timePrecision 6;
    graphFormat raw;
    runTimeModifiable true;
Best regards
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File Type: jpg U.jpg (22.2 KB, 41 views)
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Old   January 3, 2015, 05:58
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Bruno Santos
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Greetings aminem,

Uhm... I had to change the title to this thread, because it did not properly indicate to what the question was actually about.
I'm guessing here that you did not read, or at least not follow, the instructions given here: http://www.cfd-online.com/Forums/ope...-get-help.html

I say this because you want anyone on the forum to be able to look at the colourful images you've provided and the solver settings and to be able to figure out what's going on .
The following was not stated and is very important to be able to give possible suggestions as to what on digital Earth is going on :
  1. Boundary conditions: what and how goes in and what and how goes out. One wrong detail in the boundary conditions is more than enough to see supersonic speeds.
  2. Geometrical dimensions: Scale is extremely important. Several years ago I tried to simulate a house's room that was half the size of planet Earth, all because I had forgotten to divide by 1000 (namely convert millimetre to metre).
  3. Transport properties and turbulence model settings: you might say it's water and that you're using k-omega SST, but one minor mistake is more than enough to not be using water and instead be using something like helium and/or the turbulence model not actually being used.
  4. Solver output: it's what tells us if the solver is actually doing something useful or not.
Anyway, my guess is that you did not properly check the geometrical details of the original geometry and the final mesh you got for it, which is why you have a flow speed 10 to 1000 times higher than you expected.

Best regards,
Bruno
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Old   January 3, 2015, 11:21
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amine
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Hi,
I have a closed domain (without inlet and outlet)
dimensions:diameter (0.16m) high (0.23m). I don't have problem in dimensions
You can find my case here : https://www.dropbox.com/s/03u8fx0lzg...ve.tar.gz?dl=0

Thanks
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