Optimising expansion deflection nozzles for vacuum thrust

Abstract

While 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.

Air Breathing Rocket Engines and Sustainable Launch Systems

“…Because the high pressure reactants move rapidly though the combustion chamber in an air breathing engine such as this, the Hybrid AB Combustion engine uses an ignition system which runs on hydrogen and oxygen, providing a very reliable and effective ignition source. As well as investigating the use of ED nozzles for the rocket engines [6], the static tests to date have also demonstrated just how feasible it is to ignite the high speed hydrogen / air mix, thus validating yet another aspect of the Hybrid AB Combustion engine operations on the HRLM space plane. The Hybrid AB engine is essentially a closed cycle rocket engine with an additional pre-cooled turbocompressor to provide a high pressure air supply to the combustion chamber.…”