Kinetic Methods for Predicting Flow Physics of Small Thruster Expansions

Abstract : Modeling of small thruster expansions has seen a sustained development of computational methods and options over the last decade. The physics of such flows encompasses multiple length-scales from continuum to rarefied as the gas expands through the nozzle into the near-space vacuum. Moreover, with the advent of MEMS fabrication both cold and hot gas working fluids experience non-continuum effects because the surface-to-volume ratio is higher than in traditional axi-symmetric nozzles. As MEMS fabrication has improved to enable higher stagnation pressures particle methods are still relevant. However, they must be able to take advantage of the large collision rates in the early part of the expansions, rather, than be penalized by enormous computational costs of DSMC. Finally, increasing the stagnation temperature does improve thrust levels (although not efficiency), but, predicting the sustainability of the nozzle material means that particle-flow and thermal simulations must be coupled.