During spacecraft reentry, a space vehicle typically encounters flow speeds in excess of Mach 20. The spacecraft designer must accurately predict flow conditions at these extreme speeds for reasons of economy and, more importantly, for the safety of the crew and vehicle. However, these conditions can not be reliably predicted by ground-based wind tunnel experiments. Hence. numerical simulation of the hypersonic flow environment is the only reasonable alternative. Demonstration of grid size independent convergence rate for the UH multigrid method applied to a 2D multicomponent Stefan-Maxwell diffusion equation.
Plots depict residual versus the number of multigrid iterations.
Five grid sizes in each figure range from 81 to 16641 nodes. A single simulation can take over one day of CPU time on on a Cray YMP supercomputer. The primary factor that explains this poor performance is the underlying iterative method used to compute the steady state and not the work required to spatially discretize the problem. Thousands of iterations of a pseudo implicit, time marching scheme are required in the traditional NASA code. For these difficult flow problems in the hypersonic regime, however, no other technique, in general, has to date been shown to be more efficient.