IMPLICIT MULTIGRID ALGORITHMS FOR INCOMPRESSIBLE TURBULENT FLOWS ON UNSTRUCTURED GRIDS/

An implicit code for computing inviscid and viscous incompressible flo ws on unstructured grids is described. The foundation of the code is a backward Euler time discretization for which the linear system is app roximately solved at each time step with either a point implicit metho d or a preconditioned generalized minimal residual (GMRES) technique. For the GMRES calculations, several techniques are investigated for fo rming the matrix-vector product. Convergence acceleration is achieved through a multigrid scheme that uses nonnested coarse grids that are g enerated using a technique described in the present paper. Convergence characteristics are investigated and results are compared with an exa ct solution for the inviscid flow over a four-element airfoil. Viscous results, which are compared with experimental data, include the turbu lent flow over a NACA 4412 airfoil, a three-element airfoil for which Mach number effects are investigated, and three-dimensional flow over a wing with a partial-span flap. (C) 1996 Academic Press, Inc.