Edge-based multigrid and preconditioning for hybrid grids

A multigrid method has been developed for the Euler and Navier-Stokes equations on unstructured hybrid grids in two and three dimensions. The coarse grids are automatically generated from the nest grid through element collapsing. This has been used in pref-erence to a previous edge-collapsing technique to preserve as much structure as possible within semi-structured grids. The performance of the multigrid is signicantly improved through the use of Jacobi preconditioning within a Runge-Kutta iterative smoother. Re-sults are presented for a variety of two-dimensional and three-dimensional problems, both inviscid and viscous with the Spalart-Allmaras turbulence model