Performance Impact of Coolant Oxidation on Transpiration Cooling for Sharp Hypersonic Vehicles

A main limiting design consideration for hypersonic flight vehicles is surface heating. State-of-the-art thermal protection systems (TPS), such as ablative heat shields, are limited in that they require blunt geometries and often experience surface degradation through material removal. Evaporative transpiration TPS can protect sharp leading edges without experiencing surface degradation. A study is conducted investigating the effect of coolant oxidation on the performance of evaporative transpiration TPS. The study uses three-dimensional direct numerical simulation algorithms considering thermochemical nonequilibrium flow around a 3.1 mm nose tip radius flying at Mach 15 and an altitude of 30 km. Aluminum is chosen as the coolant because of its high latent heat of vaporization and low molar mass. The exothermic oxidation reactions are shown to greatly increase the incident heat flux and require over twice the coolant mass flux at the stagnation point to maintain a leading-edge temperature near the saturation temperature of the coolant. This effect is prevalent even under the nonequilibrium conditions of very slow reaction speeds, [Formula: see text] times lower than their accepted values. Therefore, oxidation reactions cannot be neglected. Understanding how coolant oxidation impacts the performance of evaporative transpiration TPS helps to inform future design of evaporative transpiration TPS.