Effects of coolant thermal reaction on chemical nonequilibrium aerothermodynamics in transpiration cooling system

Thermal protection for supersonic vehicles is essential due to the intense aerodynamic heating encountered during flight. Active cooling methods have been employed to address these thermal challenges, but the specific mechanisms by which coolant mass injection affects wall heat flux under high enthalpy conditions remain insufficiently understood. This study utilizes laminar numerical simulations to investigate the impact of various injected coolants on wall heat flux. The computational framework models high-altitude supersonic flight regimes characterized by low freestream Reynolds numbers, specifically focusing on micro-porous transpiration systems operating at low injection mass fluxes. The results indicate that coolants with lower molecular weight achieve higher injection velocities and foster stronger synergy between the velocity and temperature fields, thereby enhancing cooling efficiency. Under the investigated high-enthalpy conditions, the cooling efficiency among different coolants exhibits an approximately log-linear trend with molecular weight. Notably, hydrogen emerges as a promising coolant due to its capacity to generate relatively low reaction heat, effectively reducing wall heat flux. In contrast, methane produces significant reaction heat due to methyl oxidation, which is observed to correlate with an unfavorable local wall heat flux enhancement; however, potential numerical sensitivities at the injection boundary warrant further targeted investigation This study can provide certain support and reference for the optimal design of active thermal protection systems for supersonic vehicles.