Hi, I'm trying to solve steady Navier-Stokes for different Reynolds numbers. My options table
-dm_moose_fieldsplit_names u,p -dm_moose_nfieldsplits 2 -fieldsplit_p_dm_moose_vars pressure -fieldsplit_p_ksp_type preonly -fieldsplit_p_pc_type jacobi -fieldsplit_u_dm_moose_vars vel_x,vel_y -fieldsplit_u_ksp_type preonly -fieldsplit_u_pc_hypre_type boomeramg -fieldsplit_u_pc_type hypre -pc_fieldsplit_schur_fact_type full -pc_fieldsplit_schur_precondition selfp -pc_fieldsplit_type schur -pc_type fieldsplit works wonderfully for a low Reynolds number of 2.2. The solver performance crushes LU as I scale up the problem. However, not surprisingly this options table struggles when I bump the Reynolds number to 220. I've read that use of AIR (approximate ideal restriction) can improve performance for advection dominated problems. I've tried setting -pc_hypre_boomeramg_restriction_type 1 for a simple diffusion problem and the option works fine. However, when applying it to my field-split preconditioned Navier-Stokes system, I get immediate non-convergence: 0 Nonlinear |R| = 1.033077e+03 0 Linear |R| = 1.033077e+03 Linear solve did not converge due to DIVERGED_NANORINF iterations 0 Nonlinear solve did not converge due to DIVERGED_LINEAR_SOLVE iterations 0 Does anyone have an idea as to why this might be happening? If not, I'd take a suggestion on where to set a breakpoint to start my own investigation. Alternatively, I welcome other preconditioning suggestions for an advection dominated problem. Alex