Analysis of Transient Flow in Supersonic Micronozzles

摘要

A numerical investigation of transient supersonic flow through a two-dimensional linear micronozzle has been performed. The baseline model for the study is derived from the NASA Goddard Space Flight Center microelectromechanical-systems-based hydrogen peroxide prototype microthruster. A hyperbolic-tangent actuation profile is used to simulate the opening and closing of a microvalve with a maximum inlet stagnation pressure of 250 kPa, which generates a maximum throat Reynolds number of Re ～ 800. The complete duty cycle occurs over 1.7 ms. Numerical simulations have been conducted for expander half-angles of 10-50°, and both slip and no-slip wall boundary conditions have been examined. The propulsion scheme employs 85%-pure hydrogen peroxide as the monopropellant fuel. Simulation results have been analyzed, and thrust production as a function of time has been quantified, along with the total impulse delivered. Micronozzle impulse efficiency has also been determined based on a theoretical maximum impulse achieved by a quasi-1-D inviscid flow responding instantaneously to the actuation profile. It is found that both the flow and thrust exhibit a response lag to the time-varying inlet pressure profile. Simulations indicate that a maximum efficiency and impulse occur for an expander half-angle of 30° for the no-slip wall boundaries, and the slip simulations demonstrate a maximum plateau in the range of 20-30°; these angles are significantly larger than with traditional conical nozzle designs.