Flow field coupling between turbine and ramjet channels during turbine-based combined cycle inlet mode transition

This study investigates the flow field behavior during the mode transition of a turbine-based combined cycle (TBCC) inlet, focusing on the coupling dynamics between turbine and ramjet channels under backpressure conditions. It reveals the dual-channel interaction mechanism and identifies three distinct coupling phenomena: when both channels are started, they operate independently; when the ramjet channel is unstarted, it has no effect on the upstream flow or turbine channel; when the turbine channel is unstarted, it alters the flow structure of the ramjet channel. This study also examines flow evolution and performance parameter changes during both forward and reverse transitions. Under throttled ramjet conditions, two distinct flow behaviors emerge depending on the initial state. In forward transitions, when the inlet is starting, hysteresis occurs in the ramjet's shock train movement, and the performance trends of the turbine and ramjet channels exhibit strong symmetry. However, when the ramjet channel fails to start, the inert flow field cannot return to its original state, and this symmetry is lost.