External surfaces are exposed to high heat fluxes caused by the high-speed airflow. However, a few specific areas exist with higher heat fluxes and higher pressures. It is known that the need for high specific impulse leads to the use and storage of liquid hydrogen fuel and liquid oxygen. Heat transfer into cryogenic liquids have to be minimised by high efficient cryogenic insulation which have to be reusable many times. Compact designs are favourable as concerns mass.
Transpiration cooling offers some potential for cooling an engine cowl leading edge.
A design has to be found with minimum sensitivity to clogging and with good predictability. To this end various options for transpiration cooling will be elaborated. A mathematical-based understanding of heat and mass transfer within the leading edge will be established. Although the heat flux and pressure levels on the aft fuselage are lower, they are still high enough to exceed potentially the long-term durability of ceramic matrix composite materials. Lowering the surface temperature by active cooling would increase the lifetime of the used materials.