Experimental and Numerical Determination of Micropropulsion Device Efficiencies at Low Reynolds Numbers

Abstract

Abstract:The need for low thrust propulsion systems for maneuvers on micro-and nano-spacecraft is growing. Low thrust characteristics generally lead to low Reynolds number flows from propulsive devices that utilize nozzle expansions. Low Reynolds number flows of helium and nitrogen through a small conical nozzle and a thin-walled orifice have been investigated both numerically, using the Direct Simulation Monte Carlo technique, and experimentally, using a nano-Newton thrust stand. For throat Reynolds number less than 100, the nozzle to orifice thrust ratio is less than unity; however, the corresponding ratio of specific impulse remains greater than one for the Reynolds number range from 0. The need for low thrust propulsion systems for maneuvers on micro-and nano-spacecraft is growing. Low thrust characteristics generally lead to low Reynolds number flows from propulsive devices that utilize nozzle expansions. Low Reynolds number flows of helium and nitrogen through a small conical nozzle and a thin-walled orifice have been investigated both numerically, using the Direct Simulation Monte Carlo technique, and experimentally, using a nano-Newton thrust stand. For throat Reynolds number less than 100, the nozzle to orifice thrust ratio is less than unity; however, the corresponding ratio of specific impulse remains greater than one for the Reynolds number range from 0.02 to 200. Once the Direct Simulation Monte Carlo model results were verified using experimental thrust and mass flow data, the model was used to investigate the effects of geometrical variations on the conical nozzle's performance. At low Reynolds numbers, improvements to the specific impulse on the order of 4 to 8% were achieved through a combination of decreasing the nozzle length and increasing the nozzle expansion angle relative to the nominal experimental geometry.

Measurements and computations of mass flow and momentum flux through short tubes in rarefied gases

“…In the transitional flow regime, therefore, a thin-walled sonic orifice or a short circular tube may perform as well as a typical micronozzle. 2 Gas flows through circular orifices and short and long tubes have been rigorously studied in the past, and extensive summaries may be found in Refs. 3 and 4 and references therein.…”

Experimental and Computational Investigation of a RF Plasma Micro-Thruster

“…Computational modeling produced cold gas thrust values within 8% of those obtained experimentally, further validating the use of DSMC for orifice flows. Previous studies 13 have shown that DSMC accurately predicts cold gas thrust and specific impulse for rarefied and near-continuum flows. Errors in this study most likely stem from machining and measurement tolerances associated with the experimental orifice diameter, surface roughness, and the axi-symmetric nature of the DSMC simulations.…”

Rarefied gas electro jet (RGEJ) micro-thruster for space propulsion

“…Since microsatellites require lower thrust and cannot operate at high enough plenum pressures, the operational Reynolds number for micro-nozzles may decrease to values as low as 100, and as heat is added, the flow experiences a further decrease in Reynolds number. Micro-thrusters with low throat Reynolds number (~100) do not experience any gains from an expansion nozzle [38]. The low plenum-pressure operation condition is chosen to scale the thrust and for the additional benefit of reduced propellant storage pressure, therefore easing the propellant tank mass and valve leakage requirements [1].…”