Numerical study on the influence of surface injection on the coupled thermal effects of ablative thermal protection systems under long-duration flight conditions

Under high-speed flow conditions, surface injection exists widely in ablative thermal protection systems (TPS), and its influence on the thermal effects of TPS exhibits strong coupling characteristics. However, due to the involvement of multi-physics fields and multi-processes, available coupled numerical simulation approaches are scarce, especially for long-endurance flight conditions. In this paper, a fluid-thermal coupled numerical method for ablative TPS with surface injection is developed for long-endurance flight scenarios. Numerical simulations are performed under typical long-duration cruise conditions of high-speed vehicles to investigate the coupled thermal effects of ablative TPS with surface injection, and the mechanism by which surface injection affects the aerothermal environment and structural thermal response is clarified. Results show that a coupled equilibrium state of heat flux-temperature-pressure-injection mass flux is formed at the gas-solid interface under injection conditions. Surface injection can reduce wall heat flux by more than 60%, alter aerodynamic loads, significantly delay the internal pyrolysis process of the material by hundreds of seconds, and lower the temperature of the entire solid domain. The cooling effect induced by injection presents distinct spatiotemporal characteristics, which are mainly caused by the spatiotemporal distribution difference of injection flux resulting from different ablation and pyrolysis reaction mechanisms. This study can provide numerical tools and theoretical support for the research, design and optimization of thermal protection systems for long-endurance high-speed vehicles.