Effect of Nonequilibrium Surface Thermochemistry in Simulation of Carbon-Based Ablators

Abstract

This study demonstrates that coupling of a material thermal-response code and a flow solver using a nonequilibrium gas/surface-interaction model provides time-accurate solutions for the multidimensional ablation of carbon-based charring ablators. The material thermal-response code used in this study is the two-dimensional implicit thermal response and ablation program, which predicts the charring-material thermal response and shape change on hypersonic space vehicles. Its governing equations include total energy balance, pyrolysis-gas mass conservation, and a three-component decomposition model. The flow code solves the reacting Navier–Stokes equations using the data-parallel-line-relaxation method. Loose coupling between the material-response and flow codes is performed by solving the surface mass balance in the flow code and the surface energy balance in the material-response code. Thus, the material surface recession is predicted by finite rate gas/surface-interaction boundary conditions implemented in the flow code, and the surface temperature and the pyrolysis-gas injection rate are computed in the material-response code. Two sets of nonequilibrium gas/surface-interaction chemistry between air and the carbon surface are studied. Coupled fluid-material-response analyses of stagnation tests conducted at the NASA Ames Research Center arcjet facilities are considered. The ablating material used in these arcjet tests was phenolic impregnated carbon ablator. Computational predictions of in-depth material thermal response and surface recession are in excellent agreement with the data for conditions in which carbon recession rate is limited by species diffusion.