A new mechanism of surface ablation of charring materials for a vehicle during reentry

Coupled thermal/fluid/chemical analysis for the surface ablation of charring materials in a vehicle during hypersonic reentry has been conducted. The pyrolysis layer model is presented to simulate the thermal responses of the material, the relations of the normal shock wave are adopted to obtain the aerodynamic parameters in the boundary layer, and the counterflow diffusion model considering chemical mechanisms of hydrocarbons is proposed to solve the combustion of the pyrolysis gases. Meanwhile, the gas-solid chemical reactions of surface char are coupled with the thermal responses, the aerodynamic parameters and the combustion of the pyrolysis gases. The new equations of surface ablation for the charring materials are discretized by the central and the up-wind difference formats. A coupled mechanism of surface ablation is simulated by using our computer codes. Numerical results indicate that the consumption of oxygen in the combustion of the pyrolysis gases can protect charring materials from the surface ablation in some degree. Furthermore, selecting charring materials with larger activation energy and smaller frequency factor can effectively improve the thermal protection performance of charring materials. This study will be helpful for the design of the thermal protection system in reentry vehicles.