[fernexda]

Dear all,
I'm currently doing unsteady simulations of a vertical axis wind turbine (VAWT) with sliding meshes, cyclicAMI interface and imposed motion (solidBodyMotionFvMesh solver). And I'm going crazy trying to match my results with experimental data.

I think my problems have mainly to do with the velocity and the boundary layer. I'm using the spalart-allmaras turbulent model, and the nutUSpaldingWallFunction wall function. The problem is that the velocity on the blade boundary is not zero...

I've proceeded in two steps.

1. First I put a '

   fixedValue

   ' of (0 0 0) m/s on the blades. The boundary layer seemed ok, but the results didn't have any physical meaning...
2. After looking at some example, I've discovered the 'movingWallVelocity' to take in account the movement of the paddle. Even though the results with this BC are still bad, they make more sense. BUT the velocity on the blade is not zero ! See pictures attached.

The problems I'm facing with the 'movingWallVelocity' are:

• Wrong boundary layer
• Highly diffusive simulation (more than with a fixedValue...)
• Crazy power coefficient values

So the question is: does anyone know where could this come from ? Am I doing something wrong ? How could I get a better BL ?

Any help would be greatly appreciated !

Regards,
Daniel

P.S.: here are my configuration files:
* Solver: pimpleDyMFoam
* OF 2.1
*0/U

/*--------------------------------*- 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       volVectorField;
    location    "0";
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (9 0 0);

boundaryField
{
    AMI_FS
    {
        type            cyclicAMI;
    }
    AMI_SF
    {
        type            cyclicAMI;
    }
    Inlet
    {
        type            fixedValue;
        value           uniform (9 0 0);
    }
    Outlet
    {
        type            inletOutlet;
        inletValue      uniform (0 0 0);
        value           uniform (0 0 0);
    }
    lowerSym
    {
        type            symmetryPlane;
    }
    upperSym
    {
        type            symmetryPlane;
    }
    back
    {
        type            empty;
    }
    front
    {
        type            empty;
    }
    paddle0
    {
        type            movingWallVelocity;
        value           uniform (0 0 0);
    }
    paddle1
    {
        type            movingWallVelocity;
        value           uniform (0 0 0);
    }
    paddle2
    {
        type            movingWallVelocity;
        value           uniform (0 0 0);
    }
}

*0/p

/*--------------------------------*- 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       volScalarField;
    location    "0";
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0;

boundaryField
{
    AMI_FS
    {
        type            cyclicAMI;
        value           uniform 0;
    }
    AMI_SF
    {
        type            cyclicAMI;
        value           uniform 0;
    }
    Inlet
    {
        type            zeroGradient;
    }
    Outlet
    {
        type            fixedValue;
        value           uniform 0;
    }
    lowerSym
    {
        type            symmetryPlane;
    }
    upperSym
    {
        type            symmetryPlane;
    }
    back
    {
        type            empty;
    }
    front
    {
        type            empty;
    }
    paddle0
    {
        type            zeroGradient;
    }
    paddle1
    {
        type            zeroGradient;
    }
    paddle2
    {
        type            zeroGradient;
    }
}

*system/fvSchemes

/*--------------------------------*- 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      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

 ddtSchemes
{
  default Euler;
}

gradSchemes
{
    default fourth;
    //grad(nuTilda)	cellLimited leastSquares 1.0;
}

divSchemes
{
  default       none;
  div(phi,U) 		Gauss linearUpwindV grad(U);
  div(phi,nuTilda)      Gauss linearUpwind default;

  div((nuEff*dev(T(grad(U)))))  Gauss linear;
}
laplacianSchemes
{
    default none;
    laplacian(rAU,p) 	Gauss linear limited 0.5;
    laplacian(DnuTildaEff,nuTilda)   Gauss linear limited 0.5;
    laplacian(nuEff,U) 	Gauss linear limited 0.5;
    //for pimple : 
    laplacian(rAUf,p) 	Gauss linear limited 0.5;
    laplacian((1|A(U)),p)  Gauss linear limited 0.5;
}

interpolationSchemes
{
    interpolate(U)    	linear;
    interpolate(HbyA)	linear;
    interpolate(((1|deltaT)*rAU))  linear;
    //for pimple : 
    interpolate(U_0)	linear;
    interpolate((1|A(U)))   linear;
    interpolate(((1|deltaT)*(1|A(U))))  linear;
}

snGradSchemes
{
    default 		limited 0.5;
}

fluxRequired
{
  default 		no;
  p ;
}

*system/fvSolution

/*--------------------------------*- 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;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    pcorr
    {
        solver          GAMG;
        smoother        GaussSeidel;
        nPreSweeps      0;
        nPostSweeps     2;
        cacheAgglomeration off;
        agglomerator    faceAreaPair;
        nCellsInCoarsestLevel 10;
        mergeLevels      1;

        tolerance        1e-7;
        relTol           0;
        //tolerance        0;
        //relTol           0;
        //maxIter          1000;
    }

    p
    {
        solver          GAMG;
        smoother        GaussSeidel;
        nPreSweeps      0;
        nPostSweeps     2;
        cacheAgglomeration off;
        agglomerator    faceAreaPair;
        nCellsInCoarsestLevel 10;
        mergeLevels      1;

        tolerance        1e-7;
        relTol           0;
    }

    pFinal
    {
        solver          GAMG;
        smoother        GaussSeidel;
        nPreSweeps      0;
        nPostSweeps     2;
        cacheAgglomeration off;
        agglomerator    faceAreaPair;
        nCellsInCoarsestLevel 10;
        mergeLevels      1;
        tolerance        1e-8;
        relTol           0;
    }


    nuTilda
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance        1e-7;
        relTol           0;
    }
    nuTildaFinal
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance        1e-8;
        relTol           0;
    }
    U
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance        1e-7;
        relTol           0;
    }

    UFinal
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance        1e-8;
        relTol           0;
    }

}



relaxationFactors
{
  fields
  {
    p             0.4;
    pFinal        1;
  }
  equations
  {
    U             0.7;
    UFinal        1;
    nuTilda       0.5;
  }
}


PIMPLE
{
    correctPhi          yes;
    nOuterCorrectors    1;

    nCorrectors         3;
    nNonOrthogonalCorrectors 0;
    pRefCell            0;
    pRefValue           0;
}

PISO
{
    nCorrectors     2;
    nNonOrthogonalCorrectors 0;
    pRefCell        0;
    pRefValue       0;
}
SIMPLE
{
    nNonOrthogonalCorrectors 1;
    nCorrectors     2;
    pRefCell        0;
    pRefValue       0;

    residualControl
    {
        p               1e-5;
        U               1e-5;
        nuTilda         1e-5;
    }
}
potentialFlow
{
  nNonOrthogonalCorrectors 3;
}

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

[fernexda]

Dear all,
I've found the answer to my question:
the velocity filed is given in absolute and not in relative value. So a velocity different from zero on the paddle is totally normal, since the paddle is moving. The fluid velocity on the paddle is equal to the paddle velocity. And the fluid has no relative velocity to the paddle. So everything is logical and in order !

Regards,
Daniel

[abuabdellah.albatal]

you are good

but i have problem in verfication the results ...
all my results are different ...
i did the mesh in the ansys mesh
to fluent ..
can you tell me what is the variables in the meshing first and then in fluent for solving the case ?

thanks in advance ...

best wishes