Performance Losses in Additively Manufactured Low Thrust Nozzles

Christopher D. Tommila

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The goal of this research is to evaluate, both analytically and experimentally, the suitability of additive manufacturing in the production of small scale thruster nozzles for low thrust orbital propulsion applications. Current high temperature metallic additive manufacturing processes, like Direct Metal Laser Sintering, typically result in untreated part surfaces with higher roughness than traditional machining processes. For large scale rocket applications, nozzle wall roughness, and the associated boundary layer effects, may safely be ignored. However, in nozzles with throat diameters on the order of ten-thousandths of an inch, any viscous effects originating at the nozzle walls must be considered. It is likely that, even at the low flow Reynolds numbers exhibited in low thrust applications, the effects of viscous losses at the nozzle walls are affected by an increase in nozzle surface roughness. The first phase of this research focuses on the design and implementation of an analytic model to predict losses in thrust coefficient due to viscous effects. During the second phase, a variety of nozzle configurations are tested in a laboratory environment to determine the accuracy of the analytic model and to identify additional modes of performance loss associated with increased surface roughness.