When modeling rarefied gas flows, continuous approximation is limited by the Knudsen regime. The presented cold gas thruster for space applications is investigated for pressure values lying between 10−2 and 103 Pa. It is comprised of a subsonic funnel region, a transsonic region consisting of a ring-shaped nozzle throat and a supersonic diffuser region. Diffusive and specular / mirror reflection is used to describe the behavior of particle/wall collision in the discrete model. Simulation results are compared both with experimental data and with numerical results computed using a finite-volume method.
The transsonic flow through the nozzle throat shows very good agreement with experimental data. Simulation and experimental results emphasize the influence of various geometric factors like size and shape of the nozzle throat. Furthermore, differences in the acceleration behavior of Argon and Xenon are examined.
Results of simulations utilizing the DSMC method [Bird, 1994, Stefanov et al., 2011] with diffusively reflecting boundary conditions present the best agreement with experimental data. Any deviation seen using the finite-volume method with no-slip boundary conditions can be explained by the equilibrium gas-state near the walls [Brenner, 2005, Greenshields et al., 2007]. The non-equilibrium approach produces lower velocity gradients near the wall, especially in wall regions with high levels of surface curvature.