Studies on Effect of Interaction of Coaxial Jets on Thrust of Air-breathing Rocket
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The rocket-based combined cycle engine, which combines a rocket engine and an air-breathing engine is expected to provide higher propulsive performance than conventional rocket engines by substituting oxygen from the air for a portion of the onboard oxidizer. The exhaust nozzle is a coaxial nozzle with a converging-diverging nozzle in the center and a convergent nozzle around it, which is an unprecedented rocket engine nozzle shape. The objective of this study is to numerically analyze the flow field near the nozzle exit and to clarify the effect of the interference between the jets on the thrust for the detailed design of rockets. In this study, an airbreathing sounding rocket, which is currently under research and development at JAXA, is used as the analysis target. As a result, we obtained the calculation results of the flow field around the nozzle. When the central jet is over-expanded, the velocity and pressure distributions at the nozzle outlet change due to the mutual effect of one jet pulling in the other jet. The total thrust of the two nozzles activated simultaneously was found to be lower than the combined thrust of the two cases in which only one of the nozzles was activated individually.
