Analysis of mode transition performance for a tandem TBCC engine

The Turbine-Based Combined-Cycle (TBCC) is a favored solution for powering the future long-range high-speed vehicle. Mode transition from the low-speed propulsion system to the high-speed propulsion system is one of the most critical TBCC enabling technologies. In this paper, the airbreathing high Mach propulsion system simulation tool (HiMach) was developed for the steady-state and transient performance analysis of all modes of operation, including mode transition, for a TBCC engine. A simplified model of turbojet windmilling was incorporated to consider the shutdown process of the turbojet during mode transition. Performance analysis of mode transition for a small-scale tandem TBCC engine was conducted using HiMach. Firstly, the mode transition strategy was made based on the principle of smooth variation of thrust and total air mass flow. Secondly, the transient performance of mode transition was simulated, with the conclusion that there exists a rapid change for some key parameters during mode transition, especially when the turbojet switches to the windmilling operation mode.