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The RBCC (rocket-based combined-cycle) engine integrates a rocket engine into the flow passage of the ramjet engine, thereby significantly broadening the operating range and becoming one of the potential solutions for the reusable space transportations. The embedded rocket, as one of the core components of an RBCC engine, is strongly coupled to other components, such as the inlet and combustor, and can induce significant impacts on the inlet start behaviors. For the stable operation of the RBCC inlet, the start/unstart hysteresis characteristics and the reliable start boundaries driven by embedded rocket are experimentally and numerically studied. The results show that due to the function of embedded rocket jet, the inlet start/unstart hysteresis range of Mach number rises from Mach 1.79–1.87 to 1.85–1.90, and the back pressure hysteresis range changes from Pc/P∞ of 3.9–5.8 to 4.7–5.8. Meanwhile, during the increasing and decreasing process of the embedded rocket pressure, the inlet undergoes a transition between start and unstart, accompanied by hysteresis phenomena as well. Furthermore, three different control strategies are proposed for the start of RBCC inlet. Similar to the traditional ramjet inlets, the RBCC inlet can self-/re-start by reducing the back pressure. Particularly, owing to the synergistic effect of embedded rocket jet and back pressure, the RBCC inlet can self-/re-start by reducing the embedded rocket pressure from Procket/P∞ = 58 to 39 in the "embedded rocket dominated" cases, while the inlet self-/re-start can be achieved by increasing the rocket pressure from Procket/P∞ = 20 to 39 in the "back pressure dominated" cases. [ABSTRACT FROM AUTHOR]

The dynamic flow behaviors, as well as the propagation and coupling of regulation information, in a rocket-based combined-cycle inlet isolator during the ejector-to-ramjet mode transitions driven by different embedded rocket control methods, are numerically investigated. The key parameters of compression power, Mach number, and pressure ratio are used to illustrate the operation performance of the inlet isolator. The rocket jet induces strong shocks while inhibiting the shock/boundary layer interaction in the jet-covered region. The coupling of the rocket jet shear and back pressure is linked to the formation of wall flow separation. The parameter distributions are greatly influenced by the destruction of shock structures, which is crucial for the stability of supersonic flowfields. The continuity of the jet boundary is disrupted by the regulation of the embedded rocket, and an increase in the throttle level will further intensify the breakup. Back pressure propagation is limited by the rocket jet and is constantly matched with the jet and mainstream until the rocket's influence domain reaches stable. The "high throttle-maintaining" and "direct-shutdown" mode transitions tend to induce oscillations in the isolator compression performance. In the "direct-shutdown" mode transition, the vorticity proportion in the combustor is unstable and the flowfield disorder is high. In the "high throttle-maintaining" mode transition, the vortex generation level is relatively stable and high, while the entropy proportion fluctuates strongly and at a high level. By adopting the "medium throttle-maintaining" mode transition, the entropy and vorticity proportion levels are relatively stable, which is conducive to the stability of mode transition. [ABSTRACT FROM AUTHOR]

The spatiotemporal distribution characteristics and flow stability of a rocket-based combined-cycle (RBCC) inlet during the ejector-to-ramjet mode transition are investigated numerically. The operational pressure of the embedded rocket is adjusted to three different levels, and the time-sequences of the rocket and back pressure regulation are varied. The pressure in feature sections is monitored to reveal the coupling relationship and stability of the internal flowfield. The inlet is more adaptable to severe disturbances under the "throttle-maintaining" regulation and is susceptible under the "direct-shutdown" regulation. The severe fluctuation period is relatively short within "medium throttle-maintaining," while is lengthy within the "high throttle-maintaining." The severe fluctuation under the direct-shutdown develops with the propagation of the regulation and decays with its establishment. The ultimate flowfields driven by different time-sequences reach unanimity with the same adjustable parameters of embedded rocket and back pressure; however, the dynamic evolutions show distinct characteristics. During the mode transition, pressure "valleys" are formed in any selected sections with the rocket regulations, and "peaks" are developed in many sections due to the propagation of back pressure or the instability of the rocket jet. For the medium throttle-maintaining regulation, the effect of time-sequence on the flowfield is relatively weak. For the high throttle-maintaining regulation, the pressure disturbance rises abruptly under the rocket priority regulation, with a most severe amplitude of 100.7%. For the direct-shutdown regulation, the maximum pressure disturbance of 125% is observed within the rocket priority regulation, and the minimum disturbance occurs within the back pressure priority regulation. [ABSTRACT FROM AUTHOR]