[metaliat93]

[QUOTE=maddalena;262440]Hello everybody,
I have the same problem as above: for an airfoil at Re 1.5*10^6, cl matches well with theoretical value, while cd is two times the wanted cd. I am using kOmegaSST as implemented in OF (and not with the lowRe variation), y+ is between 30 and 110 everywhere, with an average value of 70. The fvSchemes is as follows:

This my analysis
https://sites.google.com/site/3didea...ofila-naca0012
If you want I can sent to you my project

[yanke]

Hi Aleksandr,
I'm currently trying to validate the same airfoil without much success. I'll be really grateful if you could please send me your project

Thanks
Camilo

kmy_527@hotmail.com

[sheaker]

Hello.
Drag coefficient is way too high because kOmegaSST turbulence model assumes that there is turbulent flow around entire airfoil surface. Turbulent viscosity is higher than laminar viscosity and that cause higher drag coefficient.

I wonder it there is someone who could give us a hint? Which turbulence model should we use to get a better drag force? I'm working on compressible case with NACA65(2)-415 laminar airfoil and I'm facing the same problem.

Have a nice day.
Sheaker

PS.
There is no such a turbulence models like those below in my openFoam 2.1.1 but my university professor recommend me:
gamma Re theta
kkl omega
gammaLCTM

I wonder if there is any more suitable turbulence model for airfoil case in openFoam 2.1.1 or openFoam 1.6-ext.

[afa13]

Hello All,
I am trying to simulate a flow over a NACA0012 airfoil with k-omegaSST(incompressible) at different angles of attack. On the NASA website, the study is done using a low Re(6e6) and a turbulence intensity of 0.052%. I tried first with the turbulence intensity of 0.5% (estimated from this website's tool) used 1 for nut/nu and a velocity of around 80m/s with 10 deg as an angle of attack. For the 0.5% I got a convergence however the values for the drag coefficient were far from the results by NASA; the lift coeffecients were in the range of 7%. However, when i change my boundary conditions based on the 0.052% criteria it doesnt converge and the program stops because I get extremely high values for both Cd and Cl. As for a 0 deg angle of attack, using the values of the 0.052% turbulent intensity to calculate the boundary conditions, the solution converges after 1474 iterations and i get

Cd=0.0071605
Cl=-0.000470603

My mesh is constructed using construct2d by using the dat file from the NASA website then the plot3dtofoam function and a createPatchDict.

Any help is appreciated because I have gone my ways trying to figure this thing out.

 patch walls y+ : min = 6.98209, max = 7.02351, average = 7.02168

The boundary conditions I have are as follows:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.0                                 |
|   \\  /    A nd           | Web:      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 0.00328535;

boundaryField
{
    farfield
    {
        type            freestream;
        freestreamValue           $internalField;
    }

   
    walls
    {
        type            kqRWallFunction;
        value           $internalField;
    }

     frontAndBack
    {
        type            empty;
    }
    
}


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2012                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      nut;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -1 0 0 0 0];

internalField   uniform 1.85e-5;

boundaryField
{
    farfield
        {
        type            freestream;
        freestreamValue $internalField;//uniform 9.8e-4;
        //value uniform 0.14;
        }


    walls
    {
        type            nutUSpaldingWallFunction;
        value           uniform 0;
    }

     frontAndBack
    {
        type            empty;
    }
}

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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      epsilon;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 219;

boundaryField
{
    farfield
    {
        type             freestream;
        freestreamValue     $internalField;
    }

    walls
    {
        type            omegaWallFunction;
        value           $internalField;
    }

      frontAndBack
    {
        type            empty;
    }
    
   
}


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.0                                 |
|   \\  /    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
{
    farfield
    {
        type            freestreamPressure;
        freestreamValue $internalField;
        
    }

    walls
    {
        type            zeroGradient;
    }

    frontAndBack
    {
        type            empty;
    }
}

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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.0                                 |
|   \\  /    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 (87.64789 15.4546 0);

boundaryField
{
   farfield
    {
        type            freestreamVelocity;
        freestreamValue $internalField;
    }
    
    walls
    {
        type            noSlip;
    }

    frontAndBack
    {
        type            empty;
    }
}


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

The code to calculate the lift and drag coefficients:

forces
 {
    type                forces;
    functionObjectLibs  ("libforces.so");
    outputControl       timeStep;
    outputInterval      1;
     
    patches             ( "walls" );
    pName               p;
    UName               U;
    rho             rhoInf;
    log                 true;
     
    CofR                (0.25 0 0);
     
    rhoInf              1.225;
}
 
 
forceCoeffs
{
    type                forceCoeffs;
    functionObjectLibs  ( "libforces.so" );
    outputControl       timeStep;
    outputInterval      1;
 
    patches             ( "walls" );
    pName               p;
    UName               U;
    rho             rhoInf;
    log                 true;
     
    liftDir             (.1736 0.98481 0);
    dragDir             (0.98481 .1736 0);
    CofR                (0.25 0 0);
    pitchAxis           (0 0 1);
     
    magUInf             89;
    rhoInf              1.225;
    lRef                1;
    Aref                1;
}

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  8
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         steadyState;
}

gradSchemes
{
    default         Gauss linear;

    limited         cellLimited Gauss linear 1;
    grad(U)         $limited;
    grad(k)         $limited;
    grad(omega)     $limited;
}

divSchemes
{
    default         none;

    div(phi,U)      bounded Gauss linearUpwind unlimited;

    turbulence      bounded Gauss linearUpwind limited;
    div(phi,k)      $turbulence;
    div(phi,omega)  $turbulence;
    div(phi,epsilon) $turbulence;
    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;
}

wallDist
{
    method meshWave;
}

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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.001;
        minIter          5;
        maxIter          100;
        smoother         GaussSeidel;
        nPreSweeps       1;
        nPostSweeps      3;
        nFinestSweeps    3;
        scaleCorrection true; 
        directSolveCoarsest false;
        cacheAgglomeration on;
        nCellsInCoarsestLevel 50;
        agglomerator     faceAreaPair;
        mergeLevels      1;
    }

    U
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.01;
        nSweeps          1;
    }

    k
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.01;
        nSweeps          1;
    }

    omega
    {
        solver           smoothSolver;
        smoother         GaussSeidel;
        tolerance        1e-8;
        relTol           0.01;
        nSweeps          1;
    }
}

SIMPLE
{
    nNonOrthogonalCorrectors 0;
    
    pRefCell        0;
    pRefValue       0;

    residualControl
    {
        p               1e-5;
        U               1e-5;
        "(k|omega)"     1e-5;
    }
}

relaxationFactors
{
    fields
    {
        p               0.3;
    }
    equations
    {
        "(U|k|omega)"   0.7;
        "(U|k|omega)Final" 0.7;
    }
}

cache
{
    grad(U);
}

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