[Ells96]

Hi all,

I'm trying to solve some steady pressure-driven pipe flows of Herschel-Bulkley fluids using simpleFOAM as a steady state solver. I'm finding that reaching convergence takes an incredibly long time. I've optimised the schemes and solvers so that, within each outer iteration, U converges in <10 iterations and p takes 1 or 2 iterations. Despite this, the residuals decrease at a very slow rate. Relaxation parameters of 0.7 for both U and p are the largest that I can use without the simulation blowing up.

Does anyone have experience with these types of flows using OpenFOAM and has advice on how to improve convergence?

I will post the fvSchemes and fvSolution files below. If any more info is needed let me know.

Thanks in advance.

ddtSchemes
{
    default         steadyState;
}

gradSchemes
{
    default         cellMDLimited  Gauss  linear  1;
}

divSchemes
{
    default         			none;
    div(phi,U)      			bounded  Gauss  linearUpwindV  grad(U);
    div((nuEff*dev2(T(grad(U))))) 	Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear corrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         corrected;
}

solvers
{
    p
    {
        solver          	GAMG;
        tolerance       	1e-06;
        relTol          	0.01;
        smoother        	GaussSeidel;
        nPreSweeps		    0;
        nPostSweeps		    2;
        cacheAgglomeration  	true;
        agglomerator		faceAreaPair;
        nCellsInCoarsestLevel  10;
        mergeLevels		1;
    }

    U
    {
        solver          smoothSolver;
        smoother        GaussSeidel;
        tolerance       1e-06;
        relTol          0.01;
        nSweeps         1;
    }
}

SIMPLE
{
    nNonOrthogonalCorrectors 	1;
    consistent			yes;
    /*pRefCell        		0;
    pRefValue       		0;*/
}

relaxationFactors
{
    fields
    {
        p	0.7;
    }
    equations
    {
        U	0.7;
    }
}