Combustion Efficiencies and Flameout Limits Computed for a Hypersonic Vehicle During Ascent

Abstract

Computations were performed to understand propulsion tradeoffs that occur when a hypersonic vehicle travels along an ascent trajectory. Operability limits are plotted that define allowable flight corridors on an altitude versus flight Mach number performance map. Two operability limits are set by requirements that combustion efficiency exceeds 0.90 and that flameout be avoided. Ambient gas pressure decreases during ascent, which for a fixed waverider inlet (compressor) design slows finite rate chemistry in the combustor. However, this can be offset by increases in flight Mach number and gas temperature in the combustor. New aspects of the work are that operability limits are computed for a waverider trimmed at each altitude. The University of Michigan-U.S. Air Force Research Laboratory scramjet in vehicle waverider model includes finite rate chemistry, three-dimensional mixing, ram-scram transition, and an empirical value of the flameout Damköhler number. A reduced-order modeling approach is justified (instead of computational fluid dynamics results) because all vehicle forces are computed over 1800 times to generate multidimensional performance maps. Trajectories were optimized to achieve highest combustion efficiency and avoid flameout limits.