Coupled flow field simulations of charring ablators with nonequilibrium surface chemistry

This paper describes the coupling of a Navier-Stokes solver to a material response code to simulate nonequilibrium gas-surface interactions. The Navier-Stokes solver used in this study is LeMANS, which is a three-dimensional computational fluid dynamics code that can simulate hypersonic reacting flows including thermo-chemical nonequilibrium effects. The material response code employed in this study is MOPAR, which uses the one-dimensional control volume finite-element method to model heat conduction and pyrolysis gas behavior. This coupling is demonstrated using a test case based on the Stardust sample return capsule. Coupled simulations are performed at three different trajectory conditions. The effects of the pyrolysis gas chemistry are evaluated by assuming that the gas is either in chemical equilibrium or composed entirely of non-reacting phenol. The results show that the non-reacting pyrolysis gas assumption produces higher convective heat fluxes, surface temperatures, and mass blowing rates. These effects are mainly due to the composition of the pyrolysis gas. The additional species produced by the pyrolysis gas in the chemical equilibrium case react with oxygen and nitrogen atoms in the gas-phase. This results in fewer atoms participating in the exothermic surface reactions, which reduces the heat transfer to the vehicle.