Studies on Effect of Interaction of Coaxial Jets on Thrust of Air-breathing Rocket

Abstract

It is anticipated that the rocket-based combined cycle engine, which incorporates a rocket engine and an airbreathing engine, will offer enhanced propulsive capabilities compared to conventional rocket engines. The exhaust nozzle is a coaxial nozzle comprising a convergent divergent nozzle in the center and a convergent nozzle around it. This represents an unprecedented configuration for a rocket engine nozzle. The objective of this study is to numerically analyze the flow field near the nozzle exit and to elucidate the impact of jet interference on thrust to facilitate the detailed design of rockets. In this study, an airbreathing sounding rocket, currently under research and development at JAXA, is employed as the analysis target. The resulting calculation yielded the flow field data around the nozzle. When the central jet is over-expanded, the velocity and pressure distributions at the nozzle outlet undergo alterations due to the mutual effect of one jet pulling in the other jet. The combined thrust of the two nozzles activated simultaneously was found to be lower than the sum of the individual thrusts of the two cases in which only one of the nozzles was activated. Conversely, the thrust remains constant when the central jet is under-expanded.