Numerical modeling of axisymmetric and three-dimensional flows in microelectromechanical systems nozzles

A numerical study of three-dimensional effects on the performance of a micronozzle fabricated from flat silicon wafers is performed by use of both continuum and kinetic approaches. The nozzle operates in a low-Reynolds-number regime, and viscous effects dominate the gas expansion. Thrust losses occur because the shear on the wall is greater in a flat nozzle configuration than in an axisymmetric conical nozzle. Therefore, the prediction of the micronozzle performance based on axisymmetric or two-dimensional modeling can lead to significant design errors. Comparison of simulation with recent data shows good agreement in terms of thrust predictions for cold-gas thrusters at Reynolds numbers of approximately 2 × 10².