Turbine-based combined cycle design and performance up to Mach 5.0

Abstract

The design of Turbine Based Combined Cycles (TBCCs), consisting of a gas turbine engine and ram- or scramjet, has previously been explored and a number of prototypes have been constructed. The sizing of the TBCC depends heavily on the trajectory flown by the platform, but the definition of the trajectory has been left mainly to optimisation algorithms. This paper presents a methodology that can be used in preliminary engine-airframe sizing studies and explores the impact of some trajectory choices on the performance of a TBCC for three simplified trajectories: constant-EAS climb, climb-dive, and climb-accelerate. It was found that the climb Equivalent Airspeed (EAS), rate of climb, and Top of Climb Mach number all affect the turbojet performance at Mach 2.0; the impact on the ramjet at Mach 5.0 is more noticeable in terms of required intake capture area rather than Specific Fuel Consumption and Specific Net Thrust. When climb-accelerate and climb-dive trajectories are compared to a baseline constant-EAS climb, with the same intake area and Mach 5.0 conditions, trajectories with lower climb EAS (whether climb-dive or climb-accelerate) have improved turbojet performance at Mach 2.0. The qualitative impact of trajectory choices, presented throughout this paper, can inform rudimentary trajectory design with respect to the effect on the engine performance and sizing and, consequentially, on the platform.