Schlieren depiction on flow characteristics and dynamic evolution of RBCC inlet under the combined impact of rocket jet and back pressure

Abstract

Stable and reliable operation of an RBCC inlet in the extremely wide flight speed range determines the normal operation of the whole RBCC engine. And in different modes, the interior flow characteristics and operational stability of the inlet are impacted comprehensively by both the embedded rocket jet and the back pressure. The flow characteristics and dynamic evolution of a RBCC inlet under the impacts of rocket jet and back pressure are studied by cold flow tests combined with schlieren photography. The experimental results show that: 1) The interior flowfield along the flow passage is differentiated into four distinct zones by the impact of the back pressure, named “easily disturbed zone”, “hardly disturbed zone”, “transition zone”, and “isolated zone”. As the back pressure functions independently, the pressure distribution demonstrates significant stepping characteristic propagating upstream from the “easily disturbed zone” to the “hardly disturbed zone” through the “transition zone”. 2) Low pressure rocket jet relieves the flow separation on the ramp wall, but 150% rise of the back pressure will yield an 80% pressure increase at the isolator exit. The stepping characteristics are weakened during the back pressure develops from the “easily disturbed zone” to the “hardly disturbed zone”. 3) High pressure rocket jet improves the comprehensive back pressure resistance of the RBCC inlet effectively. The pressure at the rocket exit is reduced by 33.45% and the pressure at the isolator exit is decreased by 38.04% when the rocket pressure of Procket/P∞ is increased from 0.95 to 1.91. 4) The stability of the inlet flowfield is synchronously affected by the rocket jet and the back pressure. The independent function of low back pressure at Pb/P∞=0.16 causes obviously low-frequency and wide-range oscillations of the flowfield. As the back pressure is increased by 137.5%, the axial oscillation range is significantly suppressed by 83.1%. The independent function of rocket jet causes no significant oscillation, but as the back pressure of Pb/P∞=0.38 functions collectively, the low pressure rocket jet at Procket/P∞=0.95 drives the interior flowfield return to the oscillation mode of low-frequency and wide-range. Nevertheless, the 105.3% increase of rocket pressure can decrease the axial oscillation range by 7.7%.