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Issue with pressure boundary and gravity in DPMFoam

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Old   October 12, 2015, 16:29
Default Issue with pressure boundary and gravity in DPMFoam
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Knut Erik Giljarhus
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Hello,

I have an issue with running the DPMFoam solver with a vertical outlet boundary. There does not seem to be a suitable boundary condition for the pressure in this case.
With gravity on you will get a hydrostatic pressure field in the internal domain, so setting a fixed value of zero becomes wrong.

Does anyone know how to fix this in DPMFoam? Other solvers, such as interFoam, seem to fix this by instead solving for p_rgh.

I have tried various other approaches, such as setting the outlet pressure to the hydrostatic pressure, but without success.

I notice that the tutorial cases for DPMFoam and MPPICFoam either only have horizontal boundaries or have gravity switched off.

Thanks,
Eric
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Old   October 15, 2015, 05:22
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Knut Erik Giljarhus
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I have attached two plots illustrating the issue. This is flow through a channel with a constant inlet velocity and without any particle injection.
In the first plot, I have used a fixed value for the pressure at the outlet (right boundary). Here you can clearly see the hydrostatic pressure buildup in the domain.

The second picture shows the result when I try to set the pressure to the hydrostatic pressure at the outlet.
That doesn't seem to work either.

- Eric

result_fixed.png

result_hydrostatic.png
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Old   October 28, 2017, 07:46
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Hello eric and everyone else,

i have the same problem as you. Exchanging air with water in DPMFoam and causes the exact same issue. I tried also many bc at the outlet and got, when the solver ran, a similar phenomena.
Did somebody solve the problem, or could tell me how to implement hydrostatic pressure to the DPMFoam solver?
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Old   November 1, 2017, 09:11
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So i tried some more bc combinations and extended the 0-folder a bit(pimpleFoam), leading to no change in both alternatives (simple (DPMFoam) and extended (pimpleFoam) 0-folder). I always get a similiar picture as eric (see attachement).
My example is a simple block geometry with 3 particles on the ground. The Inlet is a fixedValue and the Outlet should just let water out as it comes, which it clearly does not, looking at the screenshot. Am i making something wrong with the boundary conditions? My second assumption is that the DPMFoam Solver (pEqn.H especially) is not made for water simulations.

Following are my p and U.water codes:
p:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    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
{
    inlet
    {
        type            fixedFluxPressure;
        phi             phi.water;
        value           $internalField;
    }

    outlet
    {
        type            fixedValue;
        value           uniform 0;;
        //phi             phi.water;
        //value           $internalField;
    }
    
    upperWall
    {
        type            zeroGradient;
    }
    walls
    {
        type            zeroGradient;
        /*
        type            fixedFluxPressure;
        phi             phi.water;
        value           $internalField;
        */
    }

    sides
    {
        type            zeroGradient;
        /*
        type            fixedFluxPressure;
        phi             phi.water;
        value           $internalField;
        */
    }
}

// ************************************************************************* //
U.water:
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  4.0                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     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
{


    inlet
    {
        type            fixedValue;
        value           uniform (0.5 0 0);
        //phi             phi.water;
        //alpha           alpha.water;     
    }

    outlet
    {
        type            zeroGradient;
        /*
        type            inletOutlet;
        phi             phi.water;
        inletValue        uniform (0 0 0);
        value           uniform (0 0 0);
        */
    }
    
    upperWall
    {
        type            noSlip;
        /*
        type            inletOutlet;
        phi             phi.water;
        inletValue        uniform (0 0 0);
        value           uniform (0 0 0);
        */
        
    }

    walls
    {
        type            noSlip;
    }
    
    sides
    {
        type            noSlip;
    }
}

// ************************************************************************* //
Attached Images
File Type: jpg OutletGlyph.jpg (137.5 KB, 3 views)
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