Investigation of translation scheme turbine-based combined-cycle inlet mode transition

Abstract Smooth inlet mode transition is critical to turbine-based combined-cycle (TBCC) propulsion system. In this paper, we put forward a translation scheme TBCC inlet mode transition, that is the closing of turbine flowpath and opening of ramjet flowpath was conducted through the translation of mode transition device. The steady and unsteady flow characteristics of inlet mode transition were studied through wind tunnel tests and numerical simulations. The flow pattern and static pressure distribution from three-dimensional numerical simulations agreed well with wind tunnel tests results. According to wind tunnel tests and steady numerical simulations, smooth inlet mode transition can be achieved during translation scheme inlet mode transition. Based on the unsteady numerical simulation of inlet mode transition, as flight Mach number increased from 2.2 to 2.5, throat Mach number varied slightly from 1.35 to 1.36, which indicated that throat Mach number is not sensitive to freestream Mach number. The terminal shock wave generated from turbine flowpath oscillated around the leading edge of mode transition device until 2/4 mode and then moved downstream to turbine flowpath. In the meantime, ramjet engine took over and terminal shock wave moved from downstream ramjet flowpath to leading edge of mode transition device.