Matching mechanism analysis and comparison of typical variable cycle high-speed turbine engines

To address the significant thrust trap of Turbine-Based Combined Cycle (TBCC) engines at high Mach numbers, variable cycle High-Speed Turbine Engines (HSTE) have been proposed to extend the flight speed envelope while maintaining low-speed efficiency. However, most existing configuration studies focus on specific designs, overlooking the fundamental role of thermodynamic cycles in driving performance differences among configurations. Based on the equilibrium relationships among flow, power, pressure, and rotational speed across engine components, this study establishes equilibrium running equations for three representative HSTE configurations to characterize their distinct thermodynamic cycle features. Furthermore, from the perspective of component matching, the internal effects of the Mode Selector Valve (MSV) and bypass area on high-speed thrust performance are analyzed in detail. Using this framework, generalized principles for configuration selection and design are proposed and validated through performance simulations under different design schemes. Results show that when the MSV is open, all three configurations achieve significantly higher total mass flow and thrust output. Low Overall Pressure Ratio (OPR) schemes are more suitable for missions emphasizing high-Mach thrust, while high OPR schemes offer better low-speed efficiency. Specifically, the TBE is preferable for acceleration and climb-focused missions, the TFRE demonstrates a broader speed range advantage, and the VCE achieves optimal fuel efficiency in comprehensive conditions. This study reveals the fundamental sources of performance differences in variable cycle HSTEs and provides theoretical support and general design guidance for configuration selection across diverse mission requirements.