[ZZW]

Hi Foamers,


I am modelling water-vapour wall boiling inside a vertical pipe, using a wedge asymmetric mesh. The length is 2m, with 15.4 mm diameter.



Pipe wall heat flux is 570000w.m-2 and the average velocity at the inlet is 1m.s-1, working at 45 bar pressure. Turbulence model for both phases is k-epsilon.
The simulation runs good at the beginning, but when the vapour volume fraction be closing to 0.1 the max velocity increases rapidly to around 3m.s-1, and then the volume fraction as well.


For reference, I have attached some files here. If my question is unclear, please let me know in the comment.


Regards,
Zao


Liquid velocity code:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    location    "0";
    object      U.liquid;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform (0 0 1);

boundaryField
{
    inlet
    {
        type            mapped;
        field           U.liquid;
        setAverage      1;
        average         (0 0 1);
        interpolationScheme cell;
        value           uniform (0 0 1);
    }
    outlet
    {
        type            pressureInletOutletVelocity;
        phi             phi.liquid;
        value           uniform (0 0 1);
    }
    
    wall
    {
        type            noSlip;
    }
    front
    {
        type            wedge;
    }
    back
    {
        type            wedge;
    }

   
}


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

alphat.liquid code:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      alphat.liquid;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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

internalField   uniform 1e-8;

boundaryField
{
    inlet
    {
        type            calculated;
        value           uniform 1e-8;
    }
    outlet
    {
        type            calculated;
        value           uniform 1e-8;
    }
    
    wall
    {
        type            compressible::alphatWallBoilingWallFunction;
        otherPhase      gas;
        phaseType       liquid;
        Prt             0.85;
        /*Cmu             0.09;
        kappa           0.41;
        E               9.8;
        relax           0.01;
        dmdt            uniform 0;*/
        partitioningModel
        {
            type        Lavieville;
            alphaCrit   0.2;
        }
        nucleationSiteModel
        {
            type        LemmertChawla;
        }
        departureDiamModel
        {
            type        TolubinskiKostanchuk;
        }
        departureFreqModel
        {
            type        Cole;
        }
        value           uniform 0.01;
    }
    front
    {
        type           wedge;
    }
    back
    {
        type            wedge;
    }
   

}


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

[ZZW]

Reason found.


mu coefficients is supposed to be corrected as:

 transport
    {
        muCoeffs<8>  (0.0004282 -6.19667e-7 0 0 0 0 0 0);
        kappaCoeffs<8> (1.14518355 -0.001017 0 0 0 0 0 0);
    }

[skizzz]

where did you get the coefficients from