Mechanism and performance of supersonic mixing enhancement in rocket-based combined cycle engine ejector mode under unsteady disturbances induced by rotating detonation

To overcome the challenges of long mixing distances and limited mixing efficiency in the supersonic ejector mode of a rocket-based combined cycle engine (RBCC), this study integrates a rotating detonation rocket engine, characterized by high thermodynamic cycle efficiency and inherent periodic flow disturbances, into the RBCC configuration. With time-averaged static pressure matched at the exits of the primary and secondary streams, a comparative investigation is performed to evaluate the mixing and combustion characteristics of a steady jet and an unsteady rotating detonation jet interacting with a supersonic secondary flow. First, the effect of rotating detonation-induced unsteadiness on the supersonic mixing layer is examined under non-reacting secondary flow conditions. The results demonstrate that high-frequency disturbances generated by rotating detonation substantially enhance momentum and mass transport between the primary and secondary streams. Compared with the steady jet, this unsteady excitation mechanism increases mixing uniformity, momentum mixing effectiveness, and temperature-field uniformity by 26.14%, 4.21%, and 28.29%, respectively, while reducing the development length of the high-mixing region by approximately 20%. As a result, the system achieves a 1.27% improvement in net thrust specific impulse. Further analysis of secondary combustion indicates that, when mixing is restricted by a shortened mixing length and fuel concentration is reduced by a high entrainment ratio, the enhanced mixing induced by rotating detonation disturbances facilitates secondary combustion. Consequently, the contribution of secondary combustion to net thrust specific impulse improvement increases from 2.66% for the steady jet configuration to 3.01% with the rotating detonation jet.