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Simulation of a low-speed fan

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Old   March 23, 2012, 11:12
Default Simulation of a low-speed fan
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Attesz
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Hi all,

I'm simulating a low speed fan at idle speed. I'm getting divergence and very high values for U, p and turbulence. I have 15M cells, but only 5 layer in the BL. I think it can be problematic, however the CFX simulation works pretty good. I'm using the MRFSimpleFoam, kOmegaSST modelling. Here are my BC's:

initial conditions:
Code:
flowVelocity         (0 0 0);
pressure             0.0;
turbulentKE          0.1;
turbulentOmega       10;
turbulentEpsilon     0.001;

omega                 230.3834; //target omega angular velocity in rad/s 

#inputMode           merge
inlet Pressure
Code:
type         totalPressure;
p0        uniform 0;
U        U;
phi        phi;
rho        none;
psi        none;
gamma        1;
value        uniform 0;
inlet U
Code:
    type         pressureInletOutletVelocity;    //for use with total pressure inlet BC
    value        uniform (0 0 0);
inlet K
Code:
type        turbulentIntensityKineticEnergyInlet;
intensity    0.05;    //low intensity 5%
U        U;
phi        phi;
value        $internalField;
inlet omega
Code:
type            turbulentMixingLengthFrequencyInlet;
mixingLength        0.01;
phi            phi;
k            k;
value            $internalField;
outlet P
Code:
       type            fixedValue;
        value           uniform 0;
outlet U
Code:
    type        inletOutlet;        //for use with totalPressure BC
    inletValue    uniform (0 0 0);
    value        uniform (0 0 0);
The walls have zeroGradient types for turbulence and pressure, and fixedValue uniform (0 0 0) for U.

fvSchemes

Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.x                                 |
|   \\  /    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;
    grad(p)         Gauss linear;
    grad(U)         cellLimited Gauss linear 1;    
}

divSchemes
{
    default          Gauss upwind;
    div(phi,U)       Gauss upwind;
    div(phi,k)       Gauss upwind;
    div(phi,omega)   Gauss upwind;
    div(phi,epsilon)  Gauss upwind;
    div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
    laplacian(nuEff,U) Gauss linear corrected;
    laplacian((1|A(U)),p) Gauss linear corrected;
    laplacian(DkEff,k) Gauss linear corrected;
    laplacian(DomegaEff,omega) Gauss linear corrected;
    laplacian(DepsilonEff,epsilon) Gauss linear corrected;
    laplacian(1,p) Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
    interpolate(U)  linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no; 
    p               ;
}


// *************************************************************************
fvSolution

Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.x                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver                  GAMG;
        tolerance           1e-8;
        relTol              1e-4;
        smoother            GaussSeidel;
    nPreSweeps           0;
        nPostSweeps          2;
        cacheAgglomeration     true;
        nCellsInCoarsestLevel     10000;
        agglomerator        faceAreaPair;
        mergeLevels         1;
        maxIter             20;
    }

      
//parameters for k-omega model
  
    U
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
    nPreSweeps       0;
        nPostSweeps      2;
        tolerance        1e-7;
        relTol           0;
        minIter        1;
        maxIter         5;
    }

    k
    {
        $U;
    tolerance    1e-08;
    relTol        0;
    minIter        1;
//    maxIter        3;
    
    }

    omega
    {
        $U;
    tolerance    1e-10;
    relTol        0;
    minIter        1;
//    maxIter        3;
    }
    epsilon
    {
        $U;
    tolerance    1e-12;
    relTol        0;
    minIter        1;
//    maxIter        3;
    }
}


SIMPLE
{
    nNonOrthogonalCorrectors 5;        //because the mesh is highly not orthogonal. maximum 20, 0 is cartesian hexahedral!
    pRefCell        0;
    pRefValue       0;
    residualControl
    {
        p               1e-5;
        U               1e-5;
        "(k|epsilon|omega)" 1e-5;
    }

}

potentialFlow
{
nNonOrthogonalCorrectors 10;
}

relaxationFactors
{
    fields
    {
        p               0.3;
    }
    equations
    {
        U   0.4;
    k   0.4;
    omega   0.4;
    }
}



// ************************************************************************* //
Picture is taken at the 10th step. Velocity magnitude using logarithmic scaling! Interpolation of the fields turned off. Mesh is fine enough.

UmagBlowUp.0010.jpg

I've also tried the case using simpleFoam, so without rotation and using flowRate inlet of 1% of the operating one.
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Last edited by Attesz; March 23, 2012 at 12:02. Reason: adding pictures
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