Edge-Based Multigrid and Preconditioning for Hybrid Grids

Abstract

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 finest grid through element collapsing. This has been used in preference to a previous edge-collapsing technique to preserve as much structure as possible within semistructured grids. The performance of the multigrid is significantly improved through the use of Jacobi preconditioning within a Runge-Kutta iterative smoother. Results are presented for a variety of two-dimensional and three-dimensional problems, both inviscid and viscous, with the Spalart-Allmaras turbulence model