A series of direct-connected tests were conducted on a rotating detonation ramjet with a cylindrical isolator-combustor configuration, under the conditions of a total temperature of 860 K and Ma=2 inflow. The influence of the combustor leading edge expansion angle (θ=30°, 45°, 60°, 90°) on the propagation characteristics, operating range, and pressure distribution of detonation waves was investigated. The results indicate that the combustion mode is consistently deflagration when the expansion angle of the leading edge of the combustor is 90°. As the expansion angle gradually decreases, the combustion mode transitions towards sawtooth and hybrid mode (including single wave stage). When the expansion angle of the leading edge of the combustor is 30°, the rotating detonation exhibits the widest self-sustaining operating range and highest combustor pressure. Additionally, as the expansion angle decreases, the lower limit of the equivalence ratio for achieving the hybrid mode decreases. At the same time, the impact of combustion modes on the inflow was analyzed and it was found that the periodic high-frequency pressure oscillation in the sawtooth wave/hybrid mode combustor could cause the positioning of leading edge of the shock train in the isolator to move upstream. The hybrid mode has the most significant impact on supersonic inflow.

This study investigates the mixing enhancement mechanism and propagation characteristics of the detonation flow field of a Rotating Detonation Engine (RDE). Three-dimensional numerical simulations of a non-premixed ramjet-based RDE fueled by gaseous ethylene are performed in OpenFOAM for configurations with 15, 30, 45, and 60 orifices at a flight Mach number of 4. The results show that fuels with a stripped distribution are primarily mixed via tangential diffusion in the cold flow field. The configuration with more orifices has a better upstream mixing efficiency, whereas its downstream mixing efficiency, which is limited by the depth of penetration, is difficult to improve further. Backward Pressure Perturbations (BPPs) opposite to the propagation direction of Rotating Detonation Waves (RDWs) are produced by the reflection of the upstream oblique shock wave with the incoming stream and the hot release of local reactions after RDWs, which significantly affects the propagation mode and mixing. The RDWs propagate in the stable single-wave mode in configurations with 45 or 60 orifices and in the multi-wave mode in configurations with 30 orifices, whereas they fail in configurations with 15 orifices. Compared with that in the cold flow field, deceleration of the main flow, pressurization, and tangential velocity perturbation caused by the RDW substantially enhance the mixing efficiency. Moreover, the tangential velocity perturbations of upstream oblique shock waves and BPPs reduce the unevenness of the fuel distribution for the next cycle. This study reveals the mixing enhancement mechanism of RDWs and can contribute to the design of the injection scheme of the RDE.