Off-Design Performance Characterization of a Variable Geometry Scramjet

Aspects relating to the design and analysis of scramjet engines for peak on and off-design performance are explored in this paper. A tip-to-tail Mach 8 flowpath is developed and compared using both fixed and variable geometry inlet and combustor components to assess the off-design performance. A quasi-one-dimensional scramjet engine model, including the effects of fuel injection location, mixing length, fuel mixing efficiency, chemical production rates, heat transfer, and viscous losses is utilized to assess the effects of the geometry variations on the hydrogen finite-rate chemistry. Due to the coupled nature of hypersonic propulsion/airframe integration, realistic two-dimensional inlet and nozzle designs have been included in this analysis. The scramjet characterization is done for changes in Mach number, dynamic pressure, angle of attack, and fuel equivalence ratio. The cowl leading edge position is used to track the trailing shock to enforce a shock-on-lip constraint, while the effects of changing the fuel injector location and the second expansion angle in the combustor are assessed. The off-design performance benefits/penalties of the selected geometric variations is quantified.

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