Mission and Micronozzle Flow Analysis of a High-Temperature Chemical Micropropulsion System

摘要

Recent trends in small-scale satellites motivate the further development of the propulsion subsystem. Micro-electromechanical systems (MEMS) micronozzles provide sufficient geometries to produce impulse bits suitable for this scale of satellite. An area of concern with MEMS micronozzles is the inefficiency associated with viscous losses of the developing boundary layer. The University of Washington recently commenced research on a high- temperature propulsion system. An advantage of increased temperature levels is an increase in specific impulse. A disadvantage is an increase in Viscous effects. The present research focuses on using numerical methods to determine an area of diminishing return for increased chamber temperature conditions. initial focus is on the development of an optimum geometry which can be applied to these high- temperature gases. Using past research efforts, an expansion half angle of 30 degrees and expansion ratio of 10 are chosen. An interesting trend of the Reynolds number is observed for small to large aspect ratios. To determine optimum thrust and specific impulse efficiency, the aspect ratio is varied from 1, 5, 10, to 15. It is found that aspect ratios of 5, 10, and 15 for the same thrust level produce better results than an aspect ratio of 1. Using an aspect ratio of 10, a temperature analysis of Reynolds numbers is analyzed for chamber temperatures of 1000 to 3000 K. Although the viscous effects increase with the increase in temperature, the author proves that up to 3000 K, there is not an area of diminishing return for any of the aspect ratios in question. These results are applied to various missions for both the main and attitude- control propulsion subsystems.