UVM Theses and Dissertations
Format:
Print
Author:
Greenfield, Benjamin J.
Dept./Program:
Mechanical Engineering
Year:
2012
Degree:
MS
Abstract:
The next generation of miniaturized spacecraft (nanosats and picosats) being designed by NASA will feature masses on the order of 1-10 kg and will require unique propulsion systems capable of delivering very low impulses (~1 [mu]N-sec) to satisfy orbital maneuvering requirements, A key component on a chemically-based micropropulsion system is the supersonic micro-nozzle, whose role is to convert the thermal energy released from a combustion or chemical decomposition process into kinetic energy and thrust. The miniaturization of propulsion systems to the MEMS-scale increases the likelihood of a multiphase flow within the supersonic micro-nozzle. For example, a multiphase flow could consist of gas and liquid micro-droplets resulting from an incomplete chemical decomposition process in a monopropellant-based propulsion scheme; alternatively, for a solid propellant scheme a gas and solid particulate flow would be present. The existence of a multiphase flow has the potential to significantly alter the performance characteristics and operating efficiencies of these nozzles on the micro-scale.
In this computational study, we investigate the impact of multiphase flow states on the micro-nozzle thrust production under steady state conditions. Parametric studies are performed to delineate the various effects of droplet size (Stokes number) and concentration (mass loading) for a range of realistic operating conditions (Reynolds numbers) for supersonic micro-nozzle configurations based on MEMS geometries. Results are presented in terms of thrust production and nozzle efficiencies. It is found that the effect of a multiphase flow always reduces thrust production and that the degradation increases with mass loading of the dispersed phase. Under the most unfavorable circumstances simulated, it is found that the nozzle efficiency can be degraded by as much as 24 percent relative to the single-phase flow state. The observed results are explained in terms of relative thrust contributions of the gas and dispersed phases and the trajectories of the droplets.
In this computational study, we investigate the impact of multiphase flow states on the micro-nozzle thrust production under steady state conditions. Parametric studies are performed to delineate the various effects of droplet size (Stokes number) and concentration (mass loading) for a range of realistic operating conditions (Reynolds numbers) for supersonic micro-nozzle configurations based on MEMS geometries. Results are presented in terms of thrust production and nozzle efficiencies. It is found that the effect of a multiphase flow always reduces thrust production and that the degradation increases with mass loading of the dispersed phase. Under the most unfavorable circumstances simulated, it is found that the nozzle efficiency can be degraded by as much as 24 percent relative to the single-phase flow state. The observed results are explained in terms of relative thrust contributions of the gas and dispersed phases and the trajectories of the droplets.