[dplamp]

Hello,

My case : a cylindrical pipe, ID=4.76mm, L=71mm. I mesh just a 5° wedge. Fluid = air. Velocity at inlet = 0.11m/s, Re = 35.

I am trying to run buoyantSimpleFoam the most basic way : no turbulence, all temperatures set to 293K.

I plot the velocity profile at the outlet, and I expect a parabolic profile. It does happen, but the velocity then reduces to 1/10 of the expected value (as far as I ran the case) and the flow changes direction near the inlet and exits the pipe trough the inlet, as can be seen in the picture bellow.

I really don't know where to look, so a hint would be very welcome !




0/U :

FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    location    "0";
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0.1169496439);        // 1/8 l/min

boundaryField
{
    #includeEtc "caseDicts/setConstraintTypes"

    inlet
    {
        type            fixedValue;
        value           uniform (0 0 0.1169496439);        // 1/8 l/min
    }

    outlet
    {
        type            zeroGradient;
    }

    wallPipe
    {
        type            noSlip;
    }

    axis
    {
        type            symmetry;
    }

    front
    {
        type            wedge;
    }

    back
    {
        type            wedge;
    }
}

0/p

FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e5;

boundaryField
{
    #includeEtc "caseDicts/setConstraintTypes"

    inlet
    {
        type            fixedValue;
        value           uniform 1e5;
    }

    outlet
    {
        type            zeroGradient;
    }

    wallPipe
    {
        type            zeroGradient;
    }

    axis
    {
        type            symmetry;
    }

    front
    {
        type            wedge;
    }

    back
    {
        type            wedge;
    }
}

0/p_rgh :

FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e5;

boundaryField
{
    #includeEtc "caseDicts/setConstraintTypes"

    inlet
    {
        type            fixedValue;
        value           uniform 1e5;
    }

    outlet
    {
        type            zeroGradient;
    }

    wallPipe
    {
        type            zeroGradient;
    }

    axis
    {
        type            symmetry;
    }

    front
    {
        type            wedge;
    }

    back
    {
        type            wedge;
    }
}

0/T :

FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      T;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 1 0 0 0];

internalField   uniform 293;

boundaryField
{
    inlet
    {
        type            fixedValue;
//        value           uniform 300.15; // Ts = Tc + 17 degC
        value           uniform 293;
    }

    outlet
    {
        type            zeroGradient;
    }

    wallPipe
    {
        type            fixedValue;
//        value           uniform 283.15; // Tc = 10 degC
        value           uniform 293;
    }

    axis
    {
        type            symmetry;
    }

    front
    {
        type            wedge;
    }

    back
    {
        type            wedge;
    }
}

system/fvSchemes :

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default steadyState;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         none;

    div(phi,U)      bounded Gauss limitedLinear 0.2;
    div(phi,K)      bounded Gauss limitedLinear 0.2;
    div(phi,h)      bounded Gauss limitedLinear 0.2;
    div(phi,k)      bounded Gauss limitedLinear 0.2;
    div(phi,epsilon) bounded Gauss limitedLinear 0.2;
    div(phi,omega) bounded Gauss limitedLinear 0.2;
    div(((rho*nuEff)*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
//    default         Gauss linear orthogonal;
    default         Gauss linear uncorrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
//    default         orthogonal;
    default         uncorrected;
}

/*wallDist
{
    method meshWave;
}
*/

system/fvSolution :

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p_rgh
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.01;

        smoother         DICGaussSeidel;

    }

//    "(U|h|k|epsilon|omega)"
    "(U|h)"
    {
        solver          PBiCGStab;
        preconditioner  DILU;
        tolerance       1e-8;
        relTol          0.1;
    }

}

SIMPLE
{
//    momentumPredictor no;
    momentumPredictor yes;      // to print U residuals
    nNonOrthogonalCorrectors 0;
    pRefCell        0;
    pRefValue       0;

    residualControl
    {
        p_rgh           1e-4;
        U               1e-4;
        h               1e-4;

        // possibly check turbulence fields
//        "(k|epsilon|omega)" 1e-3;
    }
}

relaxationFactors
{
    fields
    {
        rho             1.0;
        p_rgh           0.7;
    }
    equations
    {
        U               0.3;
        h               0.3;
//        "(k|epsilon|omega)" 0.7;
    }
}

constant/thermoPhysicalProperties :

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant";
    object      thermophysicalProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectGas;
    specie          specie;
    energy          sensibleEnthalpy;
}

mixture
{
    specie
    {
        molWeight       28.96;
    }
    thermodynamics
    {
        Cp              1004.4;
        Hf              0;
    }
    transport
    {
        mu              1.831e-05;
        Pr              0.705;
    }
}

constant/turbulenceProperties :

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      RASProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

//simulationType RAS;
simulationType laminar;

RAS
{
    RASModel            kOmegaSST;

    turbulence          on;

    printCoeffs         on;
}

[jherb]

What is the direction of gravity? Perpendicular to the flow direction? If not, you can use for the p_rgh outlet boundary condition:


fixedMean, see https://github.com/OpenFOAM/OpenFOAM...ived/fixedMean

[dplamp]

U and p are set at the inlet. That's OK for U, but p should be set at the outlet instead.