Finite element model of fluid flow inside a micro-thruster

Microchannel based propulsion systems have come in handy in development of precise control and maneuvering of small spacecrafts. However it is difficult to predict the performance of the microthrusters numerically since the standard assumptions of using Navier Stokes equations break down at micro scale. A two-dimensional finite element based macroscopic model is currently being developed to incorporate the effect of slip boundary conditions as well as transition regime for reasonably high Knudsen number flow inside a microthruster. This paper documents the status of this development and will address relevant numerical issues. As a first case, a Si-micromachined solid propellant based converging-diverging microthruster nozzle, manufactured at LAASCNRS, is modeled for high temperature application using no-slip continuum. While the 2-D results obtained by this simulation are comparable to the 1-D results published in the literature, the 2-D model shows better flow details and predicts significantly higher thrust. The model is further examined for a cold microthruster of similar nozzle geometry by implementing the slip wall boundary with temperature jump wall condition for higher Knudsen Number.