3d-Navier Stokes-Periodic Conditions

Isa

Hello to everybody:

I must solve the NSE's with periodic boundary conditions, to getting this goal, I use:

-FEM: Q1/Q0. -For time discretitation: Backward Euler. -Iterative solver: * For prediction the velocity: Biconjugate Gradient, with Jacobi precondition. * For calculate the pressure: Conjugate Gradient with no precondition.

My questions are:

-How I can know that the solvers and the preconditioners I use are the rigth ones? -Must I filter the pressure solution in each time step to get out the spurious modes?

Thanks in advance and best regards Isa