3D Computation through a radial impeller

Ursenbacher

Hello,

I'm using a 3D solver to compute the flow through a radial impeller passage. To make the computation, I have the choice between 2 numerical schemes: a second order central sheme with second and fourth order numerical dissipation and a first order upwind scheme.

The problem is that I have convergence problem when I use the central scheme. The massflow and all other values oscillate.

I find a solution with the upwind scheme but the massflow seems to be smaller than with the other scheme. I asked myself whether the massflow difference between the two shemes comes from the numerical viscosity of the first order scheme. What do you think about that?

Do the oscillations I found using the second order scheme come from a supersonic region?

I've checked and in certain regions the velocity is (M=0.8 1). Near impeller entry and in diffusor outlet.

Thanks for your answer

F.Ursenbacher