Computation through radial impeller

Ursenbacher

Hello,

I'm doing a computation through a radial impeller but I have some convergence problems. The numerical scheme I use is a 2nd order central sheme with 2nd and 4th order dissipation for spatial discretisation and a 4th order Runge Kutta for time discretisation. The problem is the following:

The massflow, the efficiency, the torque,etc.. oscillate. If I reduce the CFL, the wave length of theses oscillations increases.

What can I do to avoid theses oscillations and to have a converged solution?

What are the effect of the 2nd and 4th order dissipation?

Can I suppress the oscillation by varrying theses two parameters?

Thanks for your attention,

F.Ursenbacher