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Zilić, Adis

Mechanical Engineering

MS

A computational model capable of analyzing viscous, supersonic flow in linear aerospike micro-nozzles will be discussed. Micro-nozzles are a key component in the miniaturized propulsion systems needed for next generation "nanosats" being designed by National Aeronautics and Space Administration (NASA) and Department of Defense (DoD) agencies. These spacecraft feature masses in the range of 1.0 - 20.0 kg. Owing to their reduced size, they have unique micropropulsion requirements including extremely low thrust levels and/or extremely low minimum impulse requirements for orbital maneuvers and attitude control. In this computational study we examine the performance of a micro-scale linear aerospike nozzle. The aerospike concept bas been around since the early 1970's, and it is a concept which has been typically associated with single-stage-to-orbit (SSTO) engine design. The inherent advantage of this type of nozzle is that it maintains its efficiency across a wide range of ambient back pressures and thus is referred to as an "altitude-compensating" nozzle. The defining feature of the aerospike nozzle is its utilization of free boundary reflection for flow alignment. On the micro-scale, the reduction in the number of solid wall boundaries comprising the nozzle has the potential to mitigate viscous effects which reduce performance. In this study, we numerically examine thrust performance of the linear aerospike micro-nozzle for various nozzle spike lengths and flow parameters in order to identify an optimal geometry. The sensitivity of thruster performance to the specific operating conditions will be examined combined with a Reynolds number parametric study of the flow regime. Decomposed hydrogen-peroxide is used as the monopropellant in the studies. Performance is characterized for different flow rates (Reynolds numbers) and aerospike lengths, and the impact of micro-scale viscous forces is assessed.