Flight Envelope Analysis of Hypersonic Leading-Edge Using Electron Transpiration Cooling

Electron transpiration cooling is a promising technique for protecting the sharp leading edges of a high-speed aircraft from the intense heat of hypersonic flight. This paper develops a simplified model of the energy balance at a surface that is thermionically emitting electrons and then applies this model as a boundary condition to high-fidelity numerical simulations of the flow over a 10 mm radius sphere-cone. After first validating the methodology against a high-velocity flight experiment, numerical solutions are developed for a range of flight conditions, spanning altitudes from 10 to 60 km and flight velocities from 1 to 6 km/s. A pair of steady-state leading-edge temperatures is computed at each condition, one with the incoming heat from the flow balanced by surface radiation and a second with the incoming heat balanced by both radiation and electron transpiration cooling. The electron transpiration case is significantly cooler, opening up most of the flight space compared to the radiation only case, which is limited to below Mach 8 assuming a nominal material limit of 2000 K. Comparing the results to a second set of calculations with different surface chemistry shows that electron transpiration cooling is significant in both supercatalytic and noncatalytic surfaces, though the differences between the two do not become significant until the surface temperatures are above 2500 K.