[carowjp]

I have been implementing a solver for one phase of fluid and a second phase of viscoelastic solid based on interFoam. The constitutive equation for the solid depends on the left Cauchy-Green deformation tensor (B) which is calculated by an equation (similar to an upper convective derivative):

   gradU = fvc::grad(U);
   L = gradU.T();

   fvSymmTensorMatrix BEqn
   (
       fvm::ddt(B)
     + fvm::div(phi, B)
    ==
     twoSymm(B & L)
   );

As a test case I am solving a lid drive cavity case with a viscoelastic solid disk as the second phase. The fluid velocities and behavior seems correct however I am observing 'ripples' on the surface of the disk which seem artificial (please see the attached). The solid also orbits around the cavity faster than the benchmark.

I suspect numerical diffusion from the upwind differencing scheme used in the solution of BEqn.

Sorry for the discourse but can anyone suggest alternative schemes or PISO settings which might improve this?

I am using the following:

divSchemes
{
    default         none;
    div(rho*phi,U)  Gauss limitedLinearV 1;
    div(phi,alpha)  Gauss vanLeer;
    div(phirb,alpha) Gauss interfaceCompression;
    div(phi,B) Gauss upwind;
}

and

PISO
{
    momentumPredictor yes;
    nCorrectors     3;
    nNonOrthogonalCorrectors 0;
    nAlphaCorr      1;
    nAlphaSubCycles 2;
    cAlpha          2;
}

thank you,

James