Optimising expansion deflection nozzles for vacuum thrust

Abstract

AbstractWhile expansion deflection (ED) nozzles have traditionally been considered primarily for use as altitude compensating devices to improve the performance of single stage to orbit vehicles, they also offer the potential for enhancing high altitude propulsion systems. If intended to only operate in near vacuum conditions, the complexity of analysis and inherent risks involved in the ED concept are greatly reduced. An integrated approach to the design and performance analysis of such nozzles is presented, comprising a mixture of computational fluid dynamics, the method of characteristics, and a semi-empirical model to allow full analysis of the closed wake flow-field of an ED nozzle. While it is demonstrated that the influence of the parameters used to define the throat region is critical to the successful application of the ED nozzle, it is also shown that with careful design the weight savings possible are significant. The analysis method itself is flexible and rapid, and lends itself well to incremental improvements in accuracy as the flow under consideration becomes better understood.