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-   -   Why do probes always sample the same value? (https://www.cfd-online.com/Forums/openfoam-solving/239172-why-do-probes-always-sample-same-value.html)

Ryuzaki October 24, 2021 05:56
Why do probes always sample the same value?
 
2 Attachment(s)
Hi all,
Firstly, I am simulating the cavity flow with and without doors at 0.85 Mach. I have successfully completed the "without doors" analysis. However, in with doors case, I have a problem with probes that sample pressure value at every time step. My initial pressure value is 62100Pa. After some time steps, probes start to measure the same pressure value which is equal to half of the initial value until the end of the analysis. I have tried different schemes but the results are the same. When I check the mesh quality, everything seems ok. In "without doors" case probes were quite successful to catch pressure fluctuations but "with doors" case probes don't catch the pressure fluctuations. What could be the problem?
thanks in advance..
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  v1912                                |
|  \\  /    A nd          | Website:  www.openfoam.com                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      polyBoundaryMesh;
    location    "constant/polyMesh";
    object      boundary;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

7
(
    back
    {
        type            symmetry;
        inGroups        1(symmetry);
        nFaces          393600;
        startFace      81097200;
    }
    door
    {
        type            wall;
        inGroups        1(walls);
        nFaces          75200;
        startFace      81490800;
    }
    front
    {
        type            patch;
                inGroups                1(farfield);
        nFaces          304000;
        startFace      81566000;
    }
    inlet
    {
        type            patch;
                inGroups                1(farfield);
        nFaces          6400;
        startFace      81870000;
    }
    outlet
    {
        type            patch;
                inGroups            1(farfield);
        nFaces          6400;
        startFace      81876400;
    }
    top
    {
        type            patch;
                inGroups            1(farfield);
        nFaces          304000;
        startFace      81882800;
    }
    wall
    {
        type            wall;
        inGroups        1(walls);
        nFaces          396000;
        startFace      82186800;
    }
)

// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  v1912                                |
|  \\  /    A nd          | Website:  www.openfoam.com                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    "(p|rho)"
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance      1e-6;
        relTol          0.01;
    }

    "(p|rho)Final"
    {
        $p;
        relTol          0;
    }

    "(U|k|e)"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance      1e-6;
        relTol          0.01;
    }

    "(U|k|e)Final"
    {
        $U;
        relTol          0;
    }
   
    "(U|k|B|nuTilda)"
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance      1e-7;
        relTol          0;
    }

    "(U|k|B|nuTilda)Final"
    {
      $U;
      relTol                0;
    }   
}

PIMPLE
{
    momentumPredictor yes;
    nOuterCorrectors 2;
    nCorrectors    2; // 1
    nNonOrthogonalCorrectors 1;

    pMinFactor      0.5;
    pMaxFactor      2.0;
}

relaxationFactors
{
    equations
    {
        ".*"  1;
    }
}

// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  v1912                                |
|  \\  /    A nd          | Website:  www.openfoam.com                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    location    "system";
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default        backward;
}

gradSchemes
{
    default        Gauss linear;
}

divSchemes
{
    default        none;
    div(phi,U)      Gauss linearUpwind        grad(U);
    div(phi,e)      Gauss limitedLinear 1;
    div(phi,K)      Gauss limitedLinear 1;
    div(phiv,p)    Gauss limitedLinear 1;
    div(phi,k)      Gauss limitedLinear 1;
    div(phi,B)      Gauss limitedLinear 1;
    div(B)          Gauss linear;
    div(phi,nuTilda) Gauss limitedLinear 1;
    div(((rho*nuEff)*dev2(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default        Gauss linear corrected;
}

interpolationSchemes
{
    default        linear;
}

snGradSchemes
{
    default        corrected;
}

wallDist
{
    method            meshWave;
}

// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  v1912                                |
|  \\  /    A nd          | Website:  www.openfoam.com                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    object      controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application    rhoPimpleFoam;

startFrom      latestTime;

startTime      0;

stopAt          endTime;

endTime        0.0625;

deltaT          1.76e-6;

writeControl    adjustable;

writeInterval  0.0125;

purgeWrite      0;

writeFormat    ascii;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision  6;

runTimeModifiable true;


functions
{
    #includeFunc MachNo
    #includeFunc residuals
       
        probes
        {
                type                        probes;
                libs                    ("libsampling.so");
                writeControl        runTime;
                writeInterval        1.76e-6;
               
                fields
                (
                        p
                );
               
                probeLocations
                (
                        (0.0254 0 0)
                        (0.0762 0 0)
                        (0.1270 0 0)
                        (0.1778 0 0)
                        (0.2286 0 0)
                        (0.2794 0 0)
                        (0.3302 0 0)
                        (0.3810 0 0)
                        (0.4318 0 0)
                        (0.4826 0 0)
                );
        }
}       

// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  v1912                                |
|  \\  /    A nd          | Website:  www.openfoam.com                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    location    "constant";
    object      turbulenceProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

simulationType  LES;

LES
{
        LESModel            SpalartAllmarasDDES;

        delta              vanDriest;

        printCoeffs        on;

        turbulence          on;       

        cubeRootVolCoeffs
{
    deltaCoeff      1;
}


laminarCoeffs
{
}

oneEqEddyCoeffs
{
    ck              0.07;
    ce              1.05;
}

dynOneEqEddyCoeffs
{
    ce              1.05;
    filter          simple;
}

locDynOneEqEddyCoeffs
{
    ce              1.05;
    filter          simple;
}

SmagorinskyCoeffs
{
    ce              1.05;
    ck              0.07;
}

Smagorinsky2Coeffs
{
    ce              1.05;
    ck              0.07;
    cD2              0.02;
}

spectEddyViscCoeffs
{
    ce              1.05;
    cB              8.22;
    cK1              0.83;
    cK2              1.03;
    cK3              4.75;
    cK4              2.55;
}

dynSmagorinskyCoeffs
{
    ce              1.05;
    filter          simple;
}

mixedSmagorinskyCoeffs
{
    ce              1.05;
    ck              0.07;
    filter          simple;
}

dynMixedSmagorinskyCoeffs
{
    ce              1.05;
    filter          simple;
}

LRRDiffStressCoeffs
{
    ce              1.05;
    ck              0.09;
    c1              1.8;
    c2              0.6;
}

DeardorffDiffStressCoeffs
{
    ce              1.05;
    ck              0.09;
    cm              4.13;
}

SpalartAllmarasCoeffs
{
    alphaNut        1.5;
    Cb1              0.1355;
    Cb2              0.622;
    Cw2              0.3;
    Cw3              2;
    Cv1              7.1;
    Cv2              5.0;
    CDES            0.65;
    ck              0.07;
}

SpalartAllmarasDDESCoeffs
{
    alphaNut        1.5;
    Cb1              0.1355;
    Cb2              0.622;
    Cw2              0.3;
    Cw3              2.0;
    Cv1              7.1;
    Cv2              5.0;
    CDES            0.65;
    ck              0.07;
}

SpalartAllmarasIDDESCoeffs
{
    delta  IDDESDelta;

    IDDESDeltaCoeffs
    {
        deltaCoeff      1;

        //according to src/turbulenceModels/incompressible/LES/SpalartAllmarasIDDES/IDDESDelta/IDDESDelta.C
        cw              0.15;
    }

    alphaNut        1.5;
    kappa            0.4187;
    Cb1              0.1355;
    Cb2              0.622;
    Cw2              0.3;
    Cw3              2.0;
    Cv1              7.1;
    Cv2              5.0;
    CDES            0.65;
    ck              0.07;

//These are the default values
    sigmaNut        0.66666;
    kappa          0.41;
    Cb1            0.1355;
    Cb2            0.622;
    Cv1            7.1;
    Cv2            5;
    CDES            0.65;
    ck              0.07;
    Cw2            0.3;
    Cw3            2;
    fwStar          0.424;
    cl              3.55;
    ct              1.63;

}

cubeRootVolCoeffs
{
    deltaCoeff      1;
}

PrandtlCoeffs
{
    delta          cubeRootVol;
    cubeRootVolCoeffs
    {
        deltaCoeff      1;
    }
    smoothCoeffs
    {
        delta          cubeRootVol;
        cubeRootVolCoeffs
        {
            deltaCoeff      1;
        }
        maxDeltaRatio  1.1;
    }
    Cdelta          0.158;
}

vanDriestCoeffs
{
    delta          cubeRootVol;
    cubeRootVolCoeffs
    {
        deltaCoeff      1;
    }
    smoothCoeffs
    {
        delta          cubeRootVol;
        cubeRootVolCoeffs
        {
            deltaCoeff      1;
        }
        maxDeltaRatio  1.1;
    }
    Aplus            26;
    Cdelta          0.158;
}

smoothCoeffs
        {
    delta          cubeRootVol;
    cubeRootVolCoeffs
    {
        deltaCoeff      1;
    }
    maxDeltaRatio  1.1;
        }

kappa            0.4187;

wallFunctionCoeffs
        {
    E                9;
        }

}
// ************************************************************************* //
Quote:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1912 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 1 -1 0 0 0 0];
internalField uniform (278.19 0 0);

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

wall
{
type noSlip;

}
kayma
{
type slip;
}
door
{
type noSlip;
}

back
{
type symmetry;
}
}

// ************************************************** *********************** //
Quote:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1912 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object T;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //



dimensions [0 0 0 1 0 0 0];

internalField uniform 266.53;

boundaryField
{
inlet
{
type fixedValue;
value uniform 266.53;
}

outlet
{
type zeroGradient;
}

walls
{
type zeroGradient;
}

front
{
type zeroGradient;
}

top
{
type zeroGradient;
}

back
{
type symmetry;
}
}

// ************************************************** *********************** //
Quote:
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: v1912 |
| \\ / A nd | Website: www.openfoam.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField uniform 62100;

boundaryField
{
back
{
type symmetry;
}

front
{
type zeroGradient;
}

walls
{
type zeroGradient;
}

inlet
{
type zeroGradient;
}

outlet
{
type waveTransmissive;
field p;
psi thermo:psi;
gamma 1.4;
fieldInf 62100;
lInf 1000;
value $internalField;
}
top
{
type zeroGradient;
}
}

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

shock77 October 26, 2021 04:12
Where are your probes located? An image might change.
Do the physical fields change after that timestep?


I suppose its rather not a problem with the sampling, since usually it works flawlessly.

Ryuzaki October 26, 2021 05:11
1 Attachment(s)
Firstly I would like to thank you for your reply,

My probes are located on the cavity floor (can be seen in the figure). In the "without doors" case my everything was fine, like you said probably it is not a problem with sampling...

I checked the physical fields, freestream value starts with 278m/s and suddenly drops to very small values such as 1, 2.. However, my pressure value seems half of the initial pressure value again.

I carried out another simulation using a different turbulence model and the same pressure value was measured very long time. After very long time pressure fluctuations commenced but fluctuations are about only 1-2 pascal.

Is it a good idea to extend the end time of the analysis? I'm stuck on this problem.

thanks in advance..

shock77 October 26, 2021 05:23
I have just now checked your BCs.


Things that might be a problem:


1. I see no inlet BC for U. Maybe its a copy paste error, since otherwise the simulation wouldnt even start?


2. You are setting the inlet for p to zeroGradient and the outlet to wavetransmissive. Depending on your inletBC for U, they might not form a closed system.



You should try the following: either p and U as fixedValue at the inlet and the outlet waveTransmissive for p and U or


totalPresse and pressureInletOutletVelocity for U at the inlet and for p and U waveTransmissive at the outlet or



you try a massFlowRate-BC for U at the inlet. I think then setting p to zeroGradient is fine.


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