Nonlinear analysis on thermal behavior of charring materials with surface ablation

In-depth thermal responses and surface recession of charring materials are two main performances of the thermal protection system in reentry vehicles subjected to aerodynamic heating. To explore the thermal behavior of the charring ablator, we developed a new one-dimensional pyrolysis layer model with the heat and mass transfer through charring materials undergoing decomposition and surface ablation. Taking AVCOAT composites in an Apollo capsule during reentry as an example, the calculation codes are written to simulate its nonlinear thermal behavior caused by temperature dependent thermal properties, two moving interfaces and one moving boundary. Numerical results indicate that the pyrolysis layer model is suitable for solving the problem of the thermal behavior of the charring ablator. The nonlinear analysis is essential in the calculation process although it brings oscillations, which have little influence on surface ablation and decomposition. The thermal blockage effect of the pyrolysis gas from decomposition is significant in TPS during earth entry. This study will be helpful for the design of the thermal protection system in reentry vehicles.