Novel Engineering Methodology for Decoupled Aerothermal Analysis of Hypersonic Atmospheric Entry Flows

Abstract

Analyses of thermal protection system response to atmospheric entry are generally performed in a decoupled manner where some terms in the surface balance equations are simplified. In such an approach, surface fluxes are calculated using a fluid dynamics solution of the hypersonic flowfield. These are nondimensionalized for use by a material response code, where correction terms are applied to account for the missing physics. A new method is presented here that directly includes ablation physics, thus removing the need for correction models. This approach includes the diffusion processes of ablative species in the boundary layer and nonequilibrium surface chemistry. The new approach is compared to the heritage methodology using a trajectory designed to allow molecular dissociation and vibrational energy contribution. The new methodology predicts surface temperatures with the same qualitative trend, with the largest disagreements in areas of the trajectory where nonequilibrium effects are expected to occur. The solid ablation flux and subsequent recession behavior are consistently lower for the new method, but this discrepancy in surface thermochemistry can be decreased by adopting kinetic models with more aggressive oxidation mechanisms. It is found that a large difference in computed recession does not necessarily equate to the largest difference in heat shield sizing.