Design Principles for Transpiration-Cooled Ceramic Sharp Leading Edges

Transpiration cooling is an active methodology in reducing surface heat flux for hypersonic vehicles, which offers the possibility of reducing nose bluntness and, therefore, increasing aerodynamic performance. This paper presents a numerical analysis of transpiration-cooled sharp leading edges made from ultra-high-temperature ceramics. The structural integrity of a 10 mm radius wedge leading edge is investigated numerically with regard to different coolant plenum geometries and pressurization magnitudes. It is found that the close spacing of individual plenum chambers reduces the stress in the material significantly and provides the maximum possible coolant mass flux. An optimization procedure of plenum pressure distribution is carried out using an analytical description of the porous flow in the leading edge. It is found that there exists an optimum plenum pressure that minimizes the probability of failure of the leading-edge model. Nitrogen coolant requires less pressure than helium to reach this criterion and, furthermore, requires less pressure to displace the air freestream and thus protect the leading edge from oxidation.