Parametric DNS Study of Coolant Materials for Transpiration Thermal Protection Systems Along Hypersonic Leading Edges

Recently there has been increasing interest in hypersonic flight systems, but the practical use of these systems remains limited primarily by the enormous heat loads present during atmospheric hypersonic flight. Transpiration thermal protection systems (TPS) can be used to combat large incident heat fluxes in a manner similar to ablative processes. However, transpiration TPS utilize vaporization of a replenishable liquid coolant and so experience no surface degradation. As such, transpiration TPS are reusable and capable of maintaining sharp geometries during operation. The goal of this study is to evaluate the cooling capability of transpiration TPS considering a variety of flight conditions and coolant properties. A parametric study of metal and metal oxide coolants was conducted using 3D DNS studies and self-similar 2D boundary-layer solutions. The boundary-layer solutions assumed frozen flow, while the DNS studies investigated the effects of thermochemical non-equilibrium and chemical interactions. With the results of this study suitable coolant materials may be determined for given flight conditions. Hence, a step is taken towards attaining reusable thermal protection systems for sharp leading edges with greater speed, maneuverability, and efficiency than is currently possible.