Effects of isolator throat height on flow field characteristics of RBCC engine

The adjustable isolator is a critical component for ensuring the efficient operation of RBCC engines over a wide-range of conditions. However, there is currently a lack of research on the impact of isolator throat height on engine performance, which hinders the determination of appropriate throat heights under varying inflow and combustion conditions in practical applications. To clarify the effects of throat height on engine performance and flow field characteristics, and to aid in establishing the correlation between operating conditions and throat height selection, numerical simulations and experimental studies were conducted. The differential effects of the isolator on engine performance across various combustion zones and rocket operating strategies were also examined. The research indicates that under identical inflow conditions and injection strategies, as the isolator throat height increases, the shock train shifts forward and the backpressure resistance weakens. However, the flow distortion index gradually decreases, while the total pressure recovery coefficient and combustion efficiency increase, leading to improved engine performance. To balance operational safety and efficiency, an intermediate throat configuration (with an 8.3% increase in throat height) should be used for combustion organization in the front section of the engine, while an enlarged throat structure (with a 16.7% increase in throat height) is recommended for combustion organization in the rear section. Under the rocket-ramjet mode, adjusting the throat height alters the location of peak combustor pressure. In such cases, adopting a maximum throat isolator (with a 55.6% increase in throat height) ensures a successful transition between rocket-ramjet and ramjet modes. This research provides a theoretical basis and data support for the determination of isolator throat height in practical flight.