Reordering of hybrid unstructured grids for an implicit Navier-Stokes solver based on OpenMP parallelization

Abstract

Grid reordering is an efficient way to obtain better implicit convergence speed in viscous flow simulation based on unstructured grids. When performing parallel computation on the shared memory machines, the convergence performance for solving high-Reynolds number flow with LU-SGS implicit scheme is ruined by the interface between different sub-domains divided by OpenMP parallelization. In order to improve the compatibility between OpenMP parallel environment and the implicit LU-SGS time-stepping scheme, a grid reordering method for unstructured hybrid grids is proposed. In this method, the structured-grid cells in the viscous layer near-body surface are reordered along the normal direction (like columns) and the unstructured part is reordered layer by layer according to the neighboring relations. To investigate the performance of the current implementation, turbulent flows around the RAE2822 airfoil, the NHLP-2D L1T2 multi-element airfoil configuration, the DLR-F6 wing–body–nacelle–pylon configuration and an aerospace plane has been simulated on unstructured hybrid grids. The numerical results show that the grid reordering method is an efficient and practical strategy for improving the convergence rate and the overall efficiency in the parallel computation with unstructured flow solver.