[pardoa]

Hello,

I'm simulating with interFoam a river reach of 1,5 km long x 50 m wide. The modelling setup is the following:

alpha.water

FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      alpha.water;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 0 0 0 0];

internalField   uniform 0; 

boundaryField
{
    inlet
    {
        type            variableHeightFlowRate;
        lowerBound      0;
        upperBound      1;
        value           uniform 0;
    }

    rightBank
    {
        type            zeroGradient;
    }

    atmosphere
    {
        type            inletOutlet;
        inletValue      uniform 0;
        value           uniform 0;
    }

    riverbed
    {
        type            zeroGradient;
    }

    leftBank
    {
        type            zeroGradient;
    }

    outlet
    {
        type            zeroGradient;
    }
}

p_rgh

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

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

internalField   uniform 0;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }

    rightBank
    {
        type            fixedFluxPressure;
    }

    atmosphere
    {
        type            totalPressure;
        p0              uniform 0;
    }

    riverbed
    {
        type            fixedFluxPressure;
    }

    leftBank
    {
        type            fixedFluxPressure;
    }

    outlet
    {
        type            totalPressure;
        p0              uniform 0;
    }
}

U

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            variableHeightFlowRateInletVelocity;
        flowRate        10;
        alpha           alpha.water;
        value           uniform (0 0 0);
    }

    rightBank
    {
        type            noSlip;
    }

    atmosphere
    {
        type            pressureInletOutletVelocity;
        value           uniform (0 0 0);
    }

    riverbed
    {
        type            noSlip;
    }

    leftBank
    {
        type            noSlip;
    }

    outlet
    {
        type            zeroGradient;
    }
}

Somehow, the output pressures are negative almost everywhere in the domain, except at the deepest pools that lie on the riverbed. I don't find a reason for this. I can't be related to the reference pressure (pRefValue) used for the calculations, since the top (atmosphere) and outlet BC already prescribe a reference for the pressure (zero in this case).

I'm inclined to think that the reason could be in the reference z the model uses for the calculations. The mesh contains absolute coordinates that correspond to an specific datum. This means the cell-centre coordinates of the cell zero aren't 0,0,0 but 624615.45526,195098.08678,693.4758. This cell is located on the upstream bottom of the domain, at the inlet, and its elevation is one of the highest of the mesh. Because of this, the rest of z of the domain will be smaller, which could result in negative values for pressure.

Can anyone give me a hand on this? Many thanks in advance.

Alvaro

[alexj]

Hi Alvaro,


I face the same problem with a similar setup and the negative pressure values are a problem for my case. I was wondering if you have found the reason for this?


Any help greatly appreciated.


Alex