[MichaelB88]

Hello,

I am trying to simulate a biomass fluidized bed with Geldart type A particles (zeolite particles, d=100e-06m, rho=1750 kg/m^3). I am using an axi-symmetric assumption. For now, I am first doing the model with kinetic theory off, to avoid complications. With kinetic theory on, I was getting the same problems, plus more.

I am using a fluidizing velocity of 1.5 cm/s. The actual minimum fluidization velocity for the experimental bed I'm modeling is around 0.6 cm/s. There is also a center feeding tube, from which a gas velocity will come out (a drop tube for cellulose), but for now I've set that to 0 velocity.

My problem is ripples or waves in alpha where the fluidizing gas is expelled from the bottom. I believe it is the result of numerical errors.

I have tried several different types of numerical schemes, starting with the default limitedLinear, then trying vanLeer (crashed, made no difference), QUICK (crashes and gives relatively large negative alpha values), and upwind (1st order, solved the ripple-problem but gave unrealistic answers, no bubbles).

Any ideas? Please take a look at the photos for a better look at what I mean.

Here are the fvSchemes and fvSolutions files:
fvSchemes:

ddtSchemes
{
    default         Euler;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         none;
    div(phia,Ua)    Gauss limitedLinearV 1;
    div(phib,Ub)    Gauss limitedLinearV 1;
    div(phib,k)     Gauss limitedLinear 1;
    div(phib,epsilon) Gauss limitedLinear 1;
    div(phi,alpha)  Gauss limitedLinear01 1;
    div(phir,alpha) Gauss limitedLinear01 1;
    div(phi,Theta)  Gauss limitedLinear 1;
    div(Rca)        Gauss linear;
    div(Rcb)        Gauss linear;
}

laplacianSchemes
{
    default         none;
    laplacian(nuEffa,Ua) Gauss linear corrected;
    laplacian(nuEffb,Ub) Gauss linear corrected;
    laplacian((rho*(1|A(U))),p) Gauss linear corrected;
    laplacian(alphaPpMag,alpha) Gauss linear corrected;
    laplacian(DkEff,k) Gauss linear corrected;
    laplacian(DepsilonEff,epsilon) Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

fluxRequired
{
    default         no;
    p               ;
}

fvSolution:

solvers
{
    p
    {
        solver          GAMG;
        tolerance       1e-08;
        relTol          0;
        smoother        DIC;
        nPreSweeps      0;
        nPostSweeps     2;
        nFinestSweeps   2;
        cacheAgglomeration true;
        nCellsInCoarsestLevel 10;
        agglomerator    faceAreaPair;
        mergeLevels     1;
    }

    pFinal
    {
        $p;
        tolerance       1e-08;
        relTol          0;
    }

    "(k|epsilon)"
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-05;
        relTol          0.1;
    }

    "(k|epsilon)Final"
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-05;
        relTol          0;
    }

    alpha
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-10;
        relTol          0;
    }

    alphaFinal
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-10;
        relTol          0;
    }
}

PIMPLE
{
    nCorrectors     4;
    nNonOrthogonalCorrectors 0;
    nAlphaCorr      2;
    correctAlpha    yes;
    pRefCell        0;
    pRefValue       0;
}

If you need anymore information, let me know.
Some additional information:
Turbulence off, laminar
alphaCorrector yes

Thanks!

Michael

[S choi]

Hi.
I'm conducting a simulation similar with yours and I find your post written a few years ago.
But this post has no answer.

I'm wondering whether you solve this problem and the way you solve.