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Old   April 18, 2022, 15:15
Default Boundary conditions and solver settings for buoyantSimpleFoam
  #1
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Jared Bland
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I'm trying to use buoyantSimpleFoam to "turn on" gravitational forces for an incompressible, laminar, isothermal pressure-driven flow but seem to be getting results inconsistent with simpleFoam even qualitatively with no mostly-uniform gradient of the pressure in the y-direction.



I understand that we can effectively gauge this away with using a modified definition of pressure for incompressible flow. (Driven cavity problem and https://en.wikipedia.org/wiki/Navier...pressible_flow). But I should be able to duplicate the results from simpleFoam with the correct settings and boundary conditions before moving to other properties like heat transfer and compressibility.



My test case uses a 3d + symbol with flow running from top to bottom (in the y-direction) in the + with all the walls with no allowed flow.



Any insight in how to properly set the BCs/solver properties would be greatly appreciated. Thanks for taking the time to read this.


Here are the main files related to this.



p:

Code:
  

/*--------------------------------*- C++ -*----------------------------------*\ 
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0;

boundaryField
{
    yPosFace
    {
        type            fixedValue; 
        value           300; // 300 pascals  
    }
    yNegFace
    {
        type            fixedValue;
        value           0; 
    }


    xPosFace
    {
        type            zeroGradient;
    }
    xNegFace
    {
        type            zeroGradient;
    }


    zPosFace
    {
        type            zeroGradient;
    }
    zNegFace
    {
        type            zeroGradient;
    }
    
    
    walls
    {
        type            zeroGradient;
    } 
} // boundaryField

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


p_rgh:

Code:
  

 

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

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

internalField   uniform 0;

boundaryField
{
    xPosFace
    {
        type            zeroGradient; 
    }
    xNegFace
    {
        type            zeroGradient; 
    }
    
    
    yPosFace
    {
        type            zeroGradient; 
    }
    yNegFace
    { 
        type            fixedValue;
        value           0; 
    }
    
    
    zPosFace
    {
        type            zeroGradient; 
    }
    zNegFace
    {
        type            zeroGradient; 
    }
 
    walls
    {
        type            zeroGradient; 
    }
 
}


U:

Code:
  

/*--------------------------------*- C++ -*----------------------------------*\ 
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0);

boundaryField
{
    xPosFace
    {
        type            noSlip;
    }

    xNegFace
    {
        type            noSlip;
    }

    yPosFace
    {
        type            zeroGradient;
    }
    yNegFace
    {
        type            zeroGradient;
    }
    
    zPosFace
    {
        type            noSlip;
    }
    zNegFace
    {
        type            noSlip;
    }
    
    walls
    {
        type            noSlip;
    }
}

// ************************************************************************* //
T:

Code:
  

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

dimensions      [0 0 0 1 0 0 0];

internalField   uniform 300;

boundaryField
{ 
    walls
    {
        type            fixedValue;
        value           uniform 300; // ~23 degC
    } 
    
    
    xPosFace
    {
        type            fixedValue;
        value           uniform 300; // ~23 degC
    } 
    xNegFace
    {
        type            fixedValue;
        value           uniform 300; // ~23 degC
    } 
    
    yPosFace
    {
        type            fixedValue;
        value           uniform 300; // ~23 degC
    } 
    yNegFace
    {
        type            fixedValue;
        value           uniform 300; // ~23 degC
    } 
    
    
    zPosFace
    {
        type            fixedValue;
        value           uniform 300; // ~23 degC
    } 
    zNegFace
    {
        type            fixedValue;
        value           uniform 300; // ~23 degC
    } 

}
blockMeshDict

Code:
  

/*--------------------------------*- C++ -*----------------------------------*\
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}

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

// convertToMeters 0.01;

xCenterMin 1.720000e-04;
xCenterMax 2.130000e-04;

yCenterMin 1.720000e-04;
yCenterMax 2.130000e-04;


xLeftMin -2.000000e-03;
xLeftMax 1.720000e-03;

xRightMin 2.130000e-03;
xRightMax 4.060000e-03;

 
yTopMin 2.130000e-03;
yTopMax 4.060000e-03;

yBottomMin -2.000000e-03;
yBottomMax 1.720000e-03;

zMin -2.000000e-03 ;
zMax 3.110000e-03 ;

vertices
(
    ( $xCenterMin $yCenterMin $zMin) // 0  
    ( $xCenterMax $yCenterMin $zMin) // 1 
    ( $xCenterMax $yCenterMax $zMin) // 2
    ( $xCenterMin $yCenterMax $zMin) // 3
    ( $xCenterMin $yCenterMin $zMax) // 4
    ( $xCenterMax $yCenterMin $zMax) // 5
    ( $xCenterMax $yCenterMax $zMax) // 6
    ( $xCenterMin $yCenterMax $zMax) // 7
    
    // Left leg  
    ($xLeftMin $yCenterMin $zMin)   // 8 
    ($xLeftMin $yCenterMax $zMin)   // 9
    ($xLeftMin $yCenterMin $zMax)   // 10 
    ($xLeftMin $yCenterMax $zMax)   // 11
    
    // Top leg   
    ($xCenterMax $yTopMax $zMin) // 12
    ($xCenterMin $yTopMax $zMin) // 13  
    ($xCenterMax $yTopMax $zMax) // 14
    ($xCenterMin $yTopMax $zMax) // 15 
    
    
    // Right leg   
    ($xRightMax $yCenterMin $zMin) // 16 
    ($xRightMax $yCenterMax $zMin) // 17  
    ($xRightMax $yCenterMin $zMax) // 18 
    ($xRightMax $yCenterMax $zMax) // 19  
    
    
    //Bottom leg   
    ($xCenterMin $yBottomMin $zMin) // 20
    ($xCenterMax $yBottomMin $zMin) // 21
    ($xCenterMin $yBottomMin $zMax) // 22
    ($xCenterMax $yBottomMin $zMax) // 23
    
);

blocks
(
    hex (0 1 2 3 4 5 6 7) (40 40 40) simpleGrading (1 1 1) // Center block of +
    //
    hex (8 0 3 9 10 4 7 11) (40 40 40) simpleGrading (1 1 1) // Left leg of +
    //
    hex (3 2 12 13 7 6 14 15) (40 40 40) simpleGrading (1 1 1) // Top leg of +
    //
    hex (1 16 17 2 5 18 19 6) (40 40 40) simpleGrading (1 1 1) // Right leg of +
    //
    hex (20 21 1 0 22 23 5 4) (40 40 40) simpleGrading (1 1 1) // Bottom leg of +
);




edges
(
);

boundary
(
    zPosFace
    {
        type wall;
        faces
        (
            (4 5 6 7) // center
            (10 4 7 11) // left
            (7 6 14 15) // top
            (5 18 19 6) // right
            (22 23 5 4) // bottom
        );
    }
    zNegFace
    {
        type wall;
        faces
        (
            (3 2 1 0) // center
            (9 3 0 8) // left
            (2 3 13 12) // top
            (1 2 17 16) // right
            (0 1 21 20) // bottom
        );
    }
    
    
    xPosFace
    {
        type wall;
        faces
        (
            (16 17 19 18) // right
        );
    }
    xNegFace
    {
        type wall;
        faces
        (    
            (10 11 9 8) // left 
        );
    }
    
    
    yPosFace
    {
        type patch;
        faces
        (
            (12 13 15 14) // top 
        );
    }
    yNegFace
    {
        type patch;
        faces
        (
            (20 21 23 22) // bottom
        );
    }
    
    
    walls
    {
        type wall;
        faces
        (
            (0 4 10 8) // left 
            (9 11 7 3) // left
            (3 7 15 13) // top 
            (2 12 14 6) // top
            (2 6 19 17) // right 
            (1 16 18 5) // right
            (1 5 23 21) // bottom 
            (20 22 4 0) // bottom
        );
    }
//    centerDummyPatch
//    {
//        type wall;
//      faces
//      (
//               (0 1 5 4) // to Bottom leg
//               (1 2 6 5) // to Right leg
//               
//               (4 7 3 0) // to Left leg
//               (2 3 7 6) // to Top leg
//               
//          ); 
//    }
);
fvOptions:

Code:
  

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

source1
{
    type            fixedTemperatureConstraint;
    timeStart       0;  
    // mode            uniform;
    temperature     300;
}




fvSolution

Code:
  

/*--------------------------------*- C++ -*----------------------------------*\
\*---------------------------------------------------------------------------*/
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)"
    {
        solver          PBiCGStab;
        preconditioner  DILU;
        tolerance       1e-8;
        relTol          0.1;
    }
}
 

SIMPLE
{
    momentumPredictor yes; // no;
    nNonOrthogonalCorrectors 0;
    nNonOrthogonalCorrectors 0;
    consistent      yes;

    residualControl
    {
        p               1e-2;
        p_rgh           1e-4;
        U               1e-3;
        // possibly check turbulence fields
        "(k|epsilon|omega|f|v2)" 1e-3;
    }
}

relaxationFactors
{
    fields
    {
        rho             0; // 1.0 in heatTransfer example ;
        p_rgh           0.3; // 0.7 in heatTransfer example;
        p               0.3; // 0.7 in heatTransfer example;
    }
    equations
    { 
        U               0.7;
        h               0.7;
        "(k|epsilon|omega)" 0.7; 
    }
}

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






momentumTransport:

Code:
  

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

simulationType RAS;

RAS
{
    model               kEpsilon;
    //model               kOmegaSST;

    turbulence          off; //on;

    printCoeffs         on;
}









thermophysicalProperties

Code:
  

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

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

mixture
{
    specie
    {
        molWeight       18;
    }
    thermodynamics
    {
        Cp              4183; // factor of 10^3 ?
        Hf              0; // -285.8; // 0;
    }
    transport
    {
        mu              900.0e-06;
        Pr              6.204;
    }
    
    equationOfState
    {
         rho 998; 
    }
}
Attached Images
File Type: jpg BuoyantSimpleFoamTest.jpg (12.8 KB, 16 views)
File Type: jpg BuoyantSimpleFoamTest2.jpg (11.7 KB, 14 views)
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Old   April 25, 2022, 12:55
Default
  #2
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Jared Bland
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Just wanted to add that the link to download the boundary conditions in the old thread here is now dead.



When I attempt to copy the BCs from one of the heatTransfer tutorials that has the type of BC fixedFluxPressure with the value $internalField, the pressure blows up in the middle of the sample.
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Old   April 28, 2022, 12:47
Default Reasonable Qualitative Results but not converging solution
  #3
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Jared Bland
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I got some advice offline about p_rgh, but when I run the simulation, I m getting "striping" of the velocity field that seems to come from somewhat spurious starts. I simplified the geometry to just a rectangular slab (but in 3 pieces like in my original + shape), and like in the + geometry, these stripes seem to happen due to the block discretization. I made the geomerty a little coarser, but I'm still seeing the artifacts. It seems like the velocity is along the +/- Z boundary.



Is this likely to be under the solver settings in the fvSolution file or the BCs? If I set the relaxationFactor of U to 0.9, the simulation diverges, but at 0.8 is seems decent. Lower than 0.8, I still see the stripes. Is there an adaptive relaxationFactor method I should look into?







p:

Code:
/*--------------------------------*- 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       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0;

boundaryField
{
    yPosFace
    {
        type            zeroGradient; 
    }
    yNegFace
    {
        type            fixedValue;
        value           0; 
    }


    xPosFace
    {
        type            zeroGradient;
    }
    xNegFace
    {
        type            zeroGradient;
    }


    zPosFace
    {
        type            zeroGradient;
    }
    zNegFace
    {
        type            zeroGradient;
    }
    
    
    walls
    {
        type            zeroGradient;
    }
    
}

// ************************************************************************* //
p_rgh:
Code:
/*--------------------------------*- 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       volScalarField;
    location    "0";
    object      p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0;

boundaryField
{
    xPosFace
    {
        type            zeroGradient;
        // value           $internalField;
        // type            fixedFluxPressure;
        // value           $internalField;
    }
    xNegFace
    {
        type            zeroGradient;
        //type            fixedFluxPressure;
        //value           $internalField;
    }
    
    
    yPosFace
    {
        //type            zeroGradient;
        //type            fixedFluxPressure;
        //value           $internalField;
        type            fixedValue;
        value           360;        
    }
    yNegFace
    {
        // type            fixedFluxPressure;
        // value           $internalField;
        type            fixedValue;
        value           0; 
        //value           $internalField; 
    }
    
    
    zPosFace
    {
        type            zeroGradient;
        //type            fixedFluxPressure;
        //value           $internalField;
    }
    zNegFace
    {
        type            zeroGradient;
        //type            fixedFluxPressure;
        //value           $internalField;
    }


    walls
    {
        type            zeroGradient;
        //type            fixedFluxPressure;
        //value           $internalField;
    }
 
}


// ************************************************************************* //
controlDict:
Code:
/*--------------------------------*- 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;
    location    "system";
    object      controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application     buoyantSimpleFoam;  

startFrom       startTime;

startTime        0;  

stopAt          endTime;
 
endTime          00; 

deltaT          1; 

writeControl    timeStep;

writeInterval   5;

purgeWrite      0;

writeFormat     binary; // ascii;

writePrecision  6;

writeCompression off;

timeFormat      general;

timePrecision   6;

runTimeModifiable true;


functions
{
    #includeFunc flowRatePatchpatches
        (
             xNegFace
             xPosFace
             yNegFace
             yPosFace
             zNegFace
             zPosFace
        );
        
    #includeFunc streamlines
    #includeFunc writeObjects(kEpsilon:G)
    // #includeFunc streamlines 
}

// ************************************************************************* //
fvSolution:
Code:
/*--------------------------------*- 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;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

        smoother         DICGaussSeidel;

    }
    p
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-06;
        relTol          0.01;
    }

//    pFinal
//    {
//        $p;
//        relTol          0;
//    }

    U
    {
        solver          smoothSolver;
        smoother        symGaussSeidel;
        tolerance       1e-05;
        relTol          0;
    }
     
    "(h|k|epsilon|omega)"
    {
        solver          PBiCGStab;
        preconditioner  DILU;
        tolerance       1e-8;
        relTol          0.1;
    }
}
 

SIMPLE
{
    momentumPredictor yes; // no;
    nNonOrthogonalCorrectors 0;
    nNonOrthogonalCorrectors 0;
    consistent      yes;

    residualControl
    {
        p               1e-6; // 4
        p_rgh           1e-6; // 4
        U               1e-6; // 4
        // possibly check turbulence fields
        "(k|epsilon|omega|f|v2)" 1e-3;
    }
}

relaxationFactors
{
    fields
    {
        rho             0.3;  
        p_rgh           0.3;  
        p               0.3;  
    }
    equations
    { 
        U               0.8; // 0.9 diverges slowly
        h               0.8; // 0.9
        "(k|epsilon|omega)" 0.7; // 0.9 
     //   ".*"            0.9; // 0.9 is more stable but 0.95 more convergent
    }
}

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











Edit:

Altering the U boundary conditions to more closely match those of a fixed U BC (like suggested in flow simulation with only delta pressure known) doesn't eliminate this issue.
Attached Images
File Type: jpg TestSlab_p_rgh.jpg (13.5 KB, 7 views)
File Type: jpg TestSlab_U_voxelated.jpg (13.6 KB, 6 views)

Last edited by JEBland; April 28, 2022 at 19:16. Reason: Added one more thing tried.
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Old   April 29, 2022, 12:26
Default An issue even with uniformly meshed slab
  #4
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Jared Bland
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Even with a rectangular slab when reducing the + fracture to a rectangular slab. There is striping in the magnitude of the velocity. The two versions of pressure (p, p_rgh) very quickly establish the gradient, but the velocity never seems to converge.



How can one approach the velocity field from simpleFoam under the buoyantSimpleFoam with ideal conditions (isothermal, incompressible)



blockMeshDict:

Code:
/*--------------------------------*- 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      blockMeshDict;
}

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

// convertToMeters 0.01;

xCenterMin 1.720000e-04;
xCenterMax 2.130000e-04;

yCenterMin 1.720000e-04;
yCenterMax 2.130000e-04;


xLeftMin -2.000000e-03;
xLeftMax 1.720000e-03;

xRightMin 2.130000e-03;
xRightMax 4.060000e-03;

 
yTopMin 2.130000e-03;
yTopMax 4.060000e-03;

yBottomMin -2.000000e-03;
yBottomMax 1.720000e-03;

zMin -2.000000e-03 ;
zMax 3.110000e-03 ;

vertices
(
    ( $xCenterMin $yCenterMin $zMin) // 0  
    ( $xCenterMax $yCenterMin $zMin) // 1 
    ( $xCenterMax $yCenterMax $zMin) // 2
    ( $xCenterMin $yCenterMax $zMin) // 3
    ( $xCenterMin $yCenterMin $zMax) // 4
    ( $xCenterMax $yCenterMin $zMax) // 5
    ( $xCenterMax $yCenterMax $zMax) // 6
    ( $xCenterMin $yCenterMax $zMax) // 7
    
    // Left leg  
    ($xLeftMin $yCenterMin $zMin)   // 8
 // ( 15 -4 -13) // Duplicate with center block 
 // ( 15  4 -13) // Duplicate with center block 
    ($xLeftMin $yCenterMax $zMin)   // 9
    ($xLeftMin $yCenterMin $zMax)   // 10
 // ( 15 -4  13)  // Duplicate with center block 
 // ( 15  4  13) // Duplicate with center block 
    ($xLeftMin $yCenterMax $zMax)   // 11
    
    // Top leg  
 // (-5 -4 -13) // Duplicate with center block 
 // (15 -4 -13) // Duplicate with center block 
    ($xCenterMax $yTopMax $zMin) // 12
    ($xCenterMin $yTopMax $zMin) // 13
//    ($xCenterMax $yTopMax $zMin) // 12
//    ($xCenterMin $yTopMax $zMin) // 13
 // (-5 -4  13) // Duplicate with center block 
 // (15 -4  13) // Duplicate with center block 3
    ($xCenterMax $yTopMax $zMax) // 14
    ($xCenterMin $yTopMax $zMax) // 15
//    ($xCenterMax $yTopMax $zMax) // 14
//    ($xCenterMin $yTopMax $zMax) // 15
    
    
    // Right leg  
 // (-5 -4 -13) // Duplicate with center block 
    ($xRightMax $yCenterMin $zMin) // 16 
    ($xRightMax $yCenterMax $zMin) // 17 
 // (-5  4 -13) // Duplicate with center block 
 // (-5 -4  13) // Duplicate with center block 
    ($xRightMax $yCenterMin $zMax) // 18 
    ($xRightMax $yCenterMax $zMax) // 19 
 // (-5  4  13) // Duplicate with center block 
    
    
    //Bottom leg   
    ($xCenterMin $yBottomMin $zMin) // 20
    ($xCenterMax $yBottomMin $zMin) // 21
 // ( 5   4 -13) // Duplicate with center block 
 // (-5   4 -13) // Duplicate with center block 
    ($xCenterMin $yBottomMin $zMax) // 22
    ($xCenterMax $yBottomMin $zMax) // 23
 // ( 5   4  13) // Duplicate with center block 
 // (-5   4  13) // Duplicate with center block 
    
);

blocks
( 
    hex (20 21 12 13 22 23 14 15) (15 100 100) simpleGrading (1 1 1) // Bottom leg of +
);



edges
(
);

boundary
(
    
    yPosFace
    {
        type patch;
        faces
        (
            (12 13 15 14) // top 
        );
    }
    yNegFace
    {
        type patch;
        faces
        (
            (20 21 23 22) // bottom
        );
    }
    
// (20 21 12 13 22 23 14 15)    
    walls
    {
        type wall;
        faces
        ( 
            (21 20 13 12) // nZ 
            (22 23 14 15) // pZ 
            // (22 23 14 15) // pZ 
            //
            (12 14 23 21) // pX 
            (20 22 15 13) // nX 
             
        );
    } 
);

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

fvSolution:
Code:
/*--------------------------------*- 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;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{    
     p_rgh
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.01;
        smoother         DICGaussSeidel;
    }
    
//    p
//    {
//        solver          PCG;
//        preconditioner  DIC;
//        tolerance       1e-06;
//        relTol          0.01;
//    }
//
//    pFinal
//    {
//        $p;
//        relTol          0;
//    }

    U
    {
        solver          smoothSolver;
        //smoother        symGaussSeidel;
        smoother        DILUGaussSeidel;
        tolerance       1e-05;
        relTol          0;
    }
    
//        "(k|h|epsilon|omega|f|v2)"
//    {
//        solver          PBiCGStab;
//        preconditioner  DILU;
//        tolerance       1e-8;
//        relTol          0.1;
//    }
    "(h|k|epsilon|omega)"
    {
        solver          PBiCGStab;
        preconditioner  DILU;
        tolerance       1e-8;
        relTol          0.1;
    }
}
 

SIMPLE
{
    momentumPredictor yes; // no;
    nNonOrthogonalCorrectors 0;
    nNonOrthogonalCorrectors 0;
    consistent      yes;

    residualControl
    {
//        p               1e-1; // 4
        p_rgh           1e-2; // 4
        U               1e-2; // 4
        // possibly check turbulence fields
        "(k|epsilon|omega|f|v2)" 1e-3;
    }
}

relaxationFactors
{
    fields
    {
        rho             0.3;  
        p_rgh           0.3;  
//        p               0.3;  
    }
    equations
    { 
        U               0.3; // 0.9 diverges slowly
        h               0.5; // 0.9
        "(k|epsilon|omega)" 0.5; // 0.9 
     //   ".*"            0.9; // 0.9 is more stable but 0.95 more convergent
    }
}

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



U (adapted to be normal to the input/output surfaces and to have zero gradient at the face):
Code:
/*--------------------------------*- 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       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0);

boundaryField
{
    xPosFace
    {
        type            noSlip;
    }

    xNegFace
    {
        type            noSlip;
    }

    yPosFace
    {
        // type            zeroGradient;
        type            directionMixed;
        refValue        uniform (0 0 0);
        refGradient     uniform (0 0 0);
        valueFraction        uniform (1 0 0 0 0 1);
        value        uniform (0 0 0);
    }
    yNegFace
    {
        type            zeroGradient;
    }
    
    zPosFace
    {
        type            noSlip;
    }
    zNegFace
    {
        type            noSlip;
    }
    
    walls
    {
        type            noSlip;
    }
}

// ************************************************************************* //
Attached Images
File Type: jpg buoyantSlab_U_5000_Its.jpg (15.1 KB, 5 views)
File Type: jpg buoyantSlab_p_rgh_5000_Its.jpg (7.6 KB, 4 views)
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Old   April 29, 2022, 13:07
Default
  #5
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Josh Williams
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Your pressure (0 Pa internal field) seems so small. Do you mean to make it atmospheric pressure? In simpleFoam, the flow is incompressible, so only pressure gradients are relevant. For compressible flow, e.g. buoyant solvers, the pressure, temperature and density are all linked (for example, see ideal gas law), so the absolute pressure must be used.
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Old   April 29, 2022, 13:42
Default
  #6
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Jared Bland
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Quote:
Originally Posted by joshwilliams View Post
Your pressure (0 Pa internal field) seems so small. Do you mean to make it atmospheric pressure? In simpleFoam, the flow is incompressible, so only pressure gradients are relevant. For compressible flow, e.g. buoyant solvers, the pressure, temperature and density are all linked (for example, see ideal gas law), so the absolute pressure must be used.

Thanks for the reply.



In short, yes, but I'm not entirely sure the effect when the density and temperature are fixed. Even so, when I adjust for that, there is still strong striping after 1000 iterations.







p_rgh:
Code:
/*--------------------------------*- 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       volScalarField;
    location    "0";
    object      p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0;

boundaryField
{ 
    
    yPosFace
    { 
        type            fixedValue;
        value           101685;    
//        value            360; // gauge        
    }
    yNegFace
    { 
        type            fixedValue;
        value           101325;  
    }
    
      
    walls
    {
        type            zeroGradient; 
    }
 
}


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



p:
Code:
/*--------------------------------*- 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       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 0;

boundaryField
{
    yPosFace
    {
        type            zeroGradient; 
    }
    yNegFace
    {
        type            zeroGradient; 
    }
 
    
    walls
    {
        type            zeroGradient;
    }
    
}

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



fvOptions:
Code:
/*--------------------------------*- 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;
    location    "constant";
    object      fvOptions;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

source1
{
    type            fixedTemperatureConstraint; 
    timeStart       0; 
    temperature     300;
}

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

thermophyiscalProperties:
Code:
/*--------------------------------*- 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;
    location    "constant";
    object      thermophysicalProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

mixture
{
    specie
    {
        molWeight       18;
    }
    thermodynamics
    {
        Cp              4183; // factor of 10^3 ?
        Hf              0; 
    }
    transport
    {
        mu              900.0e-06;
        Pr              6.204;
    }
    
    equationOfState
    {
         rho 998; 
    }
} 

// ************************************************************************* //
Attached Images
File Type: jpg buoyantSlab_atmospheric_U_1000_Its.jpg (28.8 KB, 6 views)
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Old   April 29, 2022, 14:23
Default
  #7
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Josh Williams
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I found an old case with buoyantPimpleFoam that reproduced same results as pimpleFoam for laminar flow in a 2D channel.
Here are the two pressure BCs. Also I had to reduce maxCo from 1 to 0.5 in the buoyant case.

p
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e5;

boundaryField
{
    inlet
    {
        type            calculated;
        value           $internalField;
    }
    walls
    {
        type            calculated;
        value           $internalField;
    }

///outlets
    OUTLET_1
    {
        type            calculated;
        value           $internalField;
    }
    frontAndBack
    {
         type           empty;
    }

}

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

p_rgh
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.2.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e5;

boundaryField
{
    inlet
    {
        type            fixedFluxPressure;
        gradient        uniform 0;
        value           uniform 1e5;
    }

    walls
    {
        type            fixedFluxPressure;
        gradient        uniform 0;
        value           uniform 1e5;
    }

///outlets
    OUTLET_1
    {
        type            totalPressure;
        p0              uniform 1e5;
        value           $internalField;
    }

    frontAndBack
    {
         type           empty;
    }

}

// ************************************************************************* //
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Old   April 29, 2022, 19:58
Default BCs and stability
  #8
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Jared Bland
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Quote:
Originally Posted by joshwilliams View Post
I found an old case with buoyantPimpleFoam that reproduced same results as pimpleFoam for laminar flow in a 2D channel.
Here are the two pressure BCs. Also I had to reduce maxCo from 1 to 0.5 in the buoyant case.

Thanks for copying that for me to see. When I try to do the same with my BCs given below, the simulation blows up, but more fundamentally I don't understand your boundary conditions. My inlet/outlet should have a fixed pressure difference across it, not necessarily just from the gravitational force, but a small difference in pressure at from inlet to outlet in addition to gravity.



I've tried a few variations, but can't seem to get results that make sense, and either the solution diverges or maintains those stripes seen before.





p:

Code:
/*--------------------------------*- 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       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e5;

boundaryField
{
    yPosFace // inlet
    {
        type            calculated;
        value           $internalField; 
    }
    
    yNegFace // outlet
    {
        type            calculated;
        value           $internalField; 
    }
    
    walls
    {
        type            calculated;
        value           $internalField; 
    }
    
}

// ************************************************************************* //
p_rgh:
Code:
/*--------------------------------*- 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       volScalarField;
    location    "0";
    object      p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e5; // 101325;

boundaryField
{
    yPosFace // inlet 
    {  
        type            fixedFluxPressure;
        gradient        uniform 0;
        value           uniform 1e5; // 101685; //           
        // value            360; // gauge
    }   

    walls
    {
        type            fixedFluxPressure;
        gradient        uniform 0;
        value           uniform 1e5;// 101325;
    }
    
    yNegFace // outlet
    { 
        type            totalPressure; // fixedValue;
        p0              uniform 1e5; // 101325;
        value           $internalField;
    }
 
}


// ************************************************************************* //
U:
Code:
/*--------------------------------*- 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       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0);

boundaryField
{
 
    yPosFace
    {
        type            directionMixed;
        refValue        uniform (0 0 0);
        refGradient     uniform (0 0 0);
        valueFraction        uniform (1 0 0 0 0 1);
        value        uniform (0 0 0);
    }
    yNegFace
    {
        type            zeroGradient;
    }
      
    walls
    {
        type            zeroGradient;
    }
}

// ************************************************************************* //
fvSolution:
Code:
/*--------------------------------*- 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;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{    
     p_rgh
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           0.01;
        smoother         DICGaussSeidel;
    }
     
    U
    {
        solver          smoothSolver;
        //smoother        symGaussSeidel;
        smoother        DILUGaussSeidel;
        tolerance       1e-05;
        relTol          0;
    }
     
    "(h|k|epsilon|omega)"
    {
        solver          PBiCGStab;
        preconditioner  DILU;
        tolerance       1e-8;
        relTol          0.1;
    }
}
 

SIMPLE
{
    momentumPredictor yes; // no;
    nNonOrthogonalCorrectors 0;
    nNonOrthogonalCorrectors 0;
    consistent      yes;

    residualControl
    { 
        p_rgh           1e-4; // 4
        U               1e-4; // 4
        // possibly check turbulence fields
        "(k|epsilon|omega|f|v2)" 1e-3;
    }
}

relaxationFactors
{
    fields
    {
        rho             0.3;  
        p_rgh           0.3;   
    }
    equations
    { 
        U               0.3; // 0.9 diverges slowly
        h               0.5; // 0.9
        "(k|epsilon|omega)" 0.5; // 0.9 
     //   ".*"            0.9; // 0.9 is more stable but 0.95 more convergent
    }
}

// ************************************************************************* //
Attached Images
File Type: jpg TestSlab_p_JW_800_its.jpg (16.2 KB, 3 views)
File Type: jpg TestSlab_p_rgh_JW_800_its.jpg (16.5 KB, 3 views)
File Type: jpg TestSlab_U_JW_800_its.jpg (19.1 KB, 4 views)
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Old   April 30, 2022, 07:49
Default
  #9
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Josh Williams
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Oh, actually I missed that part "pressure-driven" in your initial post. For pressure-driven flow, "zeroGradient" is not good for U inlet and outlet (I guess inlet and outlet are yPosFace and yNegFace from skimming your BCs quickly).


For pressure-driven (incompressible) flow, I found best results using "pressureInletVelocity" for an inlet and "pressureInletOutletVelocity" at the outlet (although I have tested reversed flow where the outlet becomes an inlet, and it performed well). This thread may be useful to you.
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Old   April 30, 2022, 11:34
Default
  #10
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Jared Bland
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Quote:
Originally Posted by joshwilliams View Post
Oh, actually I missed that part "pressure-driven" in your initial post. For pressure-driven flow, "zeroGradient" is not good for U inlet and outlet (I guess inlet and outlet are yPosFace and yNegFace from skimming your BCs quickly).


For pressure-driven (incompressible) flow, I found best results using "pressureInletVelocity" for an inlet and "pressureInletOutletVelocity" at the outlet (although I have tested reversed flow where the outlet becomes an inlet, and it performed well). This thread may be useful to you.



Thanks again. I'd tried some variants of this, but even implementing that, I still get that the solution is diverging. Attempting to start the initial velocity field in the -y direction didn't fix it either.

Looking at the documentation on totalPressure, I'm not sure I fully understand why rho is required but phi and U are optional: https://www.openfoam.com/documentati...-pressure.html
Adding the line

Code:
 

rho     rho;
to the p_rgh BCs doesn't fix anything. (I've tried it with and without the rho line in the p_rgh file)


Could the issue be that my reference height for the gravitational field is in the middle of the sample instead of the top/bottom and I haven't explicitly told the solver to shift the zero of the potential energy function?



p_rgh:

Code:
/*--------------------------------*- 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       volScalarField;
    location    "0";
    object      p_rgh;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e5; 

boundaryField
{
    yPosFace // inlet 
    { 
        type            totalPressure;   
        rho             rho; // diverges with or without this line
        p0              uniform 100360;  
        value           100360; // 360 gauge
    }   

    walls
    {
        type            fixedFluxPressure;
        gradient        uniform 0;
        value           uniform 1e5;// 101325;
    }
    
    yNegFace // outlet
    { 
        type            totalPressure;   
        rho             rho; // diverges with or without this line
        p0              uniform 1e5; // 0 Gauge
        //value           $internalField; // diverges with either value as internalField or uniform pressure
        value           uniform 1e5;
    }
 
}

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








U:

Code:
/*--------------------------------*- 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       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0);

boundaryField
{

    yPosFace
    { 
        type            pressureInletUniformVelocity; 
        value        uniform (0 0 0);
    }  
    yNegFace
    { 
        type            pressureInletOutletVelocity; 
        value        uniform (0 0 0);
    }
      
    walls
    {
        type            zeroGradient;
    }
}

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



p:

Code:
/*--------------------------------*- 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       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e5;

boundaryField
{
    yPosFace // inlet
    {
        type            calculated;
        value           $internalField; 
    }
    
    yNegFace // outlet
    {
        type            calculated;
        value           $internalField; 
    }
    
    walls
    {
        type            calculated;
        value           $internalField; 
    }
    
}

// ************************************************************************* //
Attached Images
File Type: jpg TestSlab_U_Uinletoutlet_200_its.jpg (23.0 KB, 3 views)
File Type: jpg TestSlab_p_rgh_Uinletoutlet_200_its.jpg (19.4 KB, 2 views)
File Type: jpg TestSlab_p_Uinletoutlet_200_its.jpg (17.5 KB, 2 views)
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Old   April 30, 2022, 13:15
Default
  #11
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Josh Williams
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Quote:
Originally Posted by JEBland View Post
U:

Code:
/*--------------------------------*- 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       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 0);

boundaryField
{

    yPosFace
    { 
        type            pressureInletUniformVelocity; 
        value        uniform (0 0 0);
    }  
    yNegFace
    { 
        type            pressureInletOutletVelocity; 
        value        uniform (0 0 0);
    }
      
    walls
    {
        type            zeroGradient;
    }
}

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



Did you mean for wall velocity to be zeroGradient..?
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Old   April 30, 2022, 16:32
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  #12
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Jared Bland
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Quote:
Originally Posted by joshwilliams View Post
Did you mean for wall velocity to be zeroGradient..?

Good question. I switched it to noSlip. I copied over an example from simpleFoam and reran - took 380 iterations on simpleFoam. Currently around 20,000 iterations with buoyantSimpleFoam to resolve the pressure to 2 decimal places and the velocity field to 3 decimal places. But it's at least plausible and giving the the same qualitative result.



Looking at this thread: buoyantSimpleFoam and watertank

it seems like maybe there's an issue with buoyantSimpleFoam for water instead of gases?



I'm going to play around with ideas to make it converge in fewer iterations. Thanks for your help.


Edit: Converged in 23850 to 2 decimal places in pressure in 3 in the velocity field.
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Old   May 28, 2022, 21:59
Default What are the p_rgh BCs physically?
  #13
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Jared Bland
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Staring at this some more, I learned that I can use the fvOptions to limit the max and min pressures and velocities, but I can't limit p_rgh for stability. I also learned that I don't really understand the role of p and p_rgh in buoyantSimpleFoam.



From the p.Eqn and U.Eqn files of the buoyantSimpleFoam source code it seems like p is only used for determining the density, and that this is then turned back into p_rgh, then p_rgh is used in the calculations?



Suppose instead of having the pressure at yMax > pressure at yMin in the sample above, I had it the other way around, how do I set up the BCs to know which direction the fluid will flow. If it's something I have to calculate, how can that be automated? It's simple enough for a flat bar aligned with the y-axis, but if there's an angle or a more complicated geometry, it's not as simple to calculate.



Suppose I want to determine the left-right flow through a bar at various orientations (supposing that there's a reservoir on the righthand side to take/give water as needed so the calculation is a single fluid phase):


Sample 1) /



Sample 2) ___


Sample 3) \


If I have the lefthand side connected at some given pressure above 1atm, then the righthand side connected at 1atm+gravitational effect, how can that be incorporated if buoyantSimpleFoam ignores it? For instance, there will definitely be flow from left to right in 2 and 3, but the flow in sample 1 will depend on the if the pressure on the lefthand side can overcome the gravitational contribution - how can we determine if there will be backflow?
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Old   October 7, 2022, 02:13
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Hi Jared, did you find some more explanation on this topic ? Thanks
Guillaume
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