마이크로 추진기의 유동 특성 해석

Abstract

For a micro-thruster with short duration of propulsion, thrusts in the unsteady periods, initial ignition and final depletion, need to be estimated to predict the total thrust with accuracy. In this study flow field in a micro-thruster nozzle was analyzed for unsteady and steady states to estimate the characteristic time for flow development and decay, and to compare it with simple theory. Flow characteristics were obtained using two different source conditions, time-dependent or pressure-dependent mass influx condition, because thrust is sensitively dependent on the chamber pressure. At pressure-dependent mass influx condition, characteristic time for decay was smaller than for development by about 50%. Also sought were the effects of heat loss and fabrication errors. The effect of heat loss is quite large. When heat loss was considered, total thrust was reduced by 30%. It was also confirmed that the magnitude of thrust was not sensitive to distortions, mismatch and length of the nozzle throat in the nozzle geometry. Navier-Stokes equation was directly solved using the commercial software, FLUENT6.3, for a 2D-planar and 2D-axisymmetric nozzle of 200 micron throat diameter.