An investigation of thermochemical reaction and aerodynamic ablation model on leading edges of reentry vehicles considering rarefaction effect

High-temperature airflow interacts with the surface material of the aircraft through multiple physical and chemical processes, significantly altering the aircraft's surface morphology, which consequently affects the evolution of flow structures as well as the aerodynamic and thermal characteristics of the vehicle. Accurate prediction of the ablation process during re-entry is crucial for designing thermal protection systems. Existing numerical simulations of aerodynamic ablation primarily focused on flow fields under fixed wall temperature conditions, neglecting the influences of complex chemical reactions and material property differences on the heating process and ablation morphology during ablation. This study employed the Direct Simulation Monte Carlo (DSMC) method, coupled with the wall energy conservation equation, and utilized the open-source program SPARTA to conduct a decoupled analysis of the aerodynamic heating process during vehicle re-entry. Using a cylindrical model as an example, corresponding governing equations were established separately for the decoupled processes of wall heating and model ablation. By integrating gas-gas and gas-solid chemical reactions behind the shock wave, the thermochemical reaction and aerodynamic ablation mechanisms under two-dimensional conditions were analyzed. The results indicate that the developed computable ablation model not only improves the accuracy of internal energy sampling for gas molecules behind the shock wave but also successfully reproduces ablation morphologies documented in existing literature. This model not only reproduces the difference in erosion morphology between the front and rear edges of a cylinder but also, after incorporating the amplification effect of surface roughness on aerodynamic heating, controls the relative error between the predicted retreat distance of the ball cone erosion and experimental data within 5%. This method represents the first comprehensive integration of wall material properties, variable wall-temperature effects, and surface roughness into the physical modeling of the ablation process within a DSMC framework, providing a theoretical basis and data support for deepening the understanding complex thermochemical non-equilibrium phenomena under variable wall temperatures.