Solving three-dimensional moving ablation interfaces between gas flow and porous thermal protection materials using a hybrid micro-continuum scale approach

Structural evolution of the porous surface caused by aerodynamic heating and ablation is crucial for evaluating the ablative performance of light-weight thermal protection materials for high speed vehicles. However, the numerical coupling prediction method of the flow, heat transfer, thermochemical reactions and the pore-scale structure evolution still remains limited. In this study, a hybrid micro-continuum scale approach is employed to predict this complicated coupling phenomenon for three-dimensional (3D) porous media. The results indicate that in the simulation of the oxidation ablation process of a typical carbon fibrous porous medium, the proposed method can successfully reproduce the needle-like morphology observed experimentally, revealing the gradual recession and surface roughness formation caused by surface heterogeneity. Moreover, under high-temperature flow conditions where the reaction rate is much larger than the mass-transfer rate due to convection and diffusion, the incoming oxygen gas can be consumed rapidly at the flow/porous media interface. This fast consumption is found to be dominant, resulting in a low oxygen supply condition at the gas–solid interface and a non-linear ablation recession rate. The recession rate is found to reach its maximum value of 13.05 μm/s, followed by a gradual decline to 8.35 μm/s. The proposed hybrid micro-continuum multiscale modeling approach can potentially offer valuable pore-scale insights into the ablation behavior of porous media, thereby enhancing the predictive accuracy for thermal protection systems.