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increasing volume fraction in closed domain with compressibleInterFoam

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Old   May 14, 2014, 12:58
Smile increasing volume fraction in closed domain with compressibleInterFoam
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Victor-S. Eberhart
Join Date: Oct 2011
Posts: 34
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Hi Foamers!

I managed to extend the compressibleInterFoam solver by a time varying acceleration which, in my case, simulates a periodic motion and is provided by a file containing the time-acceleration tuples.

As you can see in the excerpt of my accFoam.C, I only introduced the acceleration in z-axis direction and defined a vector called acc which also contains the gravitation:
Code:
    while (runTime.run())
    {
        #include "readTimeControls.H"
        #include "CourantNo.H"
        #include "setDeltaT.H"

        runTime++;

        // --- time varying acceleration
        interpolationTable<scalar> lookup("acceleration.dat");

        scalar  acc_X = 0.0;
        scalar  acc_Y = 0.0;
        scalar  acc_Z = lookup(runTime.value());//timeSeriesAcceleration;
       
        Info<< "Acceleration in z-direction = " << acc_Z << nl << endl;

        const dimensionedScalar gunits("gunits", dimensionSet(0,1,-2,0,0,0,0), 1.0);
        dimensionedVector acc=g + vector(acc_X,acc_Y,acc_Z)*gunits;

        Info<< "Time = " << runTime.timeName() << nl << endl;

        // --- Pressure-velocity PIMPLE corrector loop
        while (pimple.loop())
In order to take the acceleration into account I added the acceleration multiplied by my mixture density to the UEqn.H file:
Code:
    fvVectorMatrix UEqn
    (
        fvm::ddt(rho, U)
      + fvm::div(rhoPhi, U)
      + turbulence->divDevRhoReff(U)
      - rho*acc
    );
Also, I extended the energy equation in the TEqn.H file as follows:
Code:
   fvScalarMatrix TEqn
    (
        fvm::ddt(rho, T)
      + fvm::div(rhoPhi, T)
      - fvm::laplacian(twoPhaseProperties.alphaEff(turbulence->mut()), T)
      + (
            fvc::div(fvc::absolute(phi, U), p)
          + fvc::ddt(rho, K) + fvc::div(rhoPhi, K)
          - rho * (acc & U)
        )
My test case, a closed test tube filled with 50% liquid sodium and 50% air "shaken" along the longitudinal axis according to a prescribed oscillating motion, yields good results for the liquid phase kinetic energy compared to a CFX case. However, during the simulation, the total liquid phase volume fraction defined by the initial filling level (0.5) is constantly increasing and reached a value of 0.58 so far. I have a suspicion that it has something to do with the compressibility of my fluids.

Speaking of which, I have doubts about the assigned value of R in my thermophysical properties for sodium. I had no idea how to calculate it, so I looked at the thermophysicalProperties.mercury from the compressibleMultiphaseInterFoam damBreak4Phase tutorial case and took a similar value, somy thermophysicalProperties.sodium looks like that:
Code:
thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectFluid;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    specie
    {
        nMoles          1;
        molWeight       22.99;
    }
    equationOfState
    {
        R               5000;
        rho0            852;
    }
    thermodynamics
    {
        Cp              1277;
        Hf              0;
    }
    transport
    {
        mu              0.000264;
        Pr              0.00496;
    }
}
I scanned the forum but only found threads related to decreasing alpha values. Maybe someone of you has already run into that problem before and found a solution for it.

Thanks a lot,
Victor
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