Transient Simulations of 3-D Supersonic Micronozzle Flow

A numerical investigation of transient performance of 3D linear micronozzles has been performed. The baseline model for the study is derived from the NASA/Goddard Space Flight Center MEMS-based hydrogen peroxide micro-thruster prototype. The 3D micronozzles investigated here have depths of 25μm, 50μm, 100μm, and 150μm and employ expanders with a 30° half-angle. A hyperbolic-tangent actuation profile is used to model the opening of a microvalve in order to simulate start-up of the thruster. The inlet stagnation pressure when the valve is fully opened is 250kPa and generates a maximum throat Reynolds number of Re_max ∼ 800. The complete actuation occurs over 0.55ms and is followed by 0.25ms of steady-state operation. The propulsion scheme employs 85% pure hydrogen peroxide as a monopropellant. 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-1D 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 are compared to previous 2D results and indicate that thrust per unit nozzle depth, impulse, and efficiency increase with nozzle depth and approach the 2D results for nozzle depths greater than 150μm.