Parametric Study of Transpiration Cooling Using Oxides for Sharp Hypersonic Leading Edges

Recent escalating interest in the development of highly maneuverable hypersonic vehicles demands sharp leading edges. However, sharp leading edges induce severe aerothermal conditions where conventional passive or ablative thermal protection systems fail to protect the leading edge. Here, we numerically demonstrate transpiration cooling employing oxide coolants as a new alternative system to thermally protect sharp leading edges. We parametrically characterize the performance of transpiration cooling for various coolant properties, flight conditions, and leading edge radii using a semi-analytic boundary-layer model validated with third-order direct numerical simulations. We further utilize direct numerical simulation to examine the impact of the thermochemical behavior of oxide vapors with the external hypersonic flow on transpiration cooling. Our findings do not readily align with an optimal set of material properties for transpiration cooling. Instead, certain coolant properties are more appropriate for various flight conditions and leading edge sizes. Our results also demonstrate that the thermochemical interactions between the oxide vapors and the external hypersonic flow have a negligible impact on the performance of transpiration cooling. Our study provides numerical frameworks to evaluate the performance of transpiration cooling and optimize the coolant properties for various flight conditions to protect sharp leading edges, which are paramount across hypersonic applications.