Drag force: ShirgaonkarIB

Hi every one,

I tried to run a settling simulation (similar to the settlingTestMPI) with the IB-Solver and found that the particle doesnt settle as it should be (Stokes as comparison). So I had a look at the calculation of the drag force and I think there is a mistake in the equations.

(1) volVectorField h = nufField*fvc::laplacian(U_)-fvc::grad(p_);
...
(2) drag += h[cellI]*h.mesh().V()[cellI];

I think both terms in equation (1) (nufField*fvc::laplacian(U_) and fvc::grad(p_)) should be multiplied with the density of the fluid.

As I understand equation (1) is derived from the momentum equation of the fluid, so in order do get a force in equation (2) (drag force) I have to use mu instead of nu for the first term in equation (1) .
-> mu = density*nu

Furthermore OpenFOAM normalises the pressure with the density (and also the gradient????). So again, in order to get a force in equation (2) I have to multiply the pressure gradient with the density.

With these changes still the dynamic behaviour of the particle is not correct, but at least the settling velocity almost matches.

Regards,
Yansan