Scramjet Performance with Nonuniform Flow and Swept Nozzles

Numerical simulations are presented that compare the specific impulse of a generic inlet-fueled uniform-compression and nonuniform-compression scramjet over the flight Mach number range of 7-12 with a constant freestream dynamic pressure trajectory of 100 kPa. Both engine configurations have identical inlet contraction ratio, inlet to nozzle area ratio, and combustor and nozzle geometries. The results show that the specific impulse in the nonuniform-compression scramjet is higher than the uniform-compression scramjet at each flight condition. The increase in specific impulse for Mach 8, 9, 10, 11, and 12 are 165, 178, 96, 74, and 15 s, respectively. Both the uniform- and nonuniform-compression engines unstarted at the Mach 7 condition. In addition, two three-dimensional swept-nozzle configurations (45 and 60 deg) are integrated into the nonuniform-compression engine to investigate an idea of coupling the nonuniform flow with a nonuniform expansion nozzle to improve performance. The 45 deg results show no change in specific impulse at Mach 8-11 and a 50 s improvement at Mach 12. The 60 deg configuration has less specific impulse at each flight condition, except Mach 12. The thermal loads are reduced by 15 and 30% for the 45 and 60 deg configurations at each flight condition. The findings provide new insight into how nonuniform compression with swept nozzles can provide an additional degree of freedom in the design of fixed-geometry scramjets that have robust performance over a range of flight conditions.