Comparison of Computed Free Thruster Plume Expansion to Experiments

Abstract

As ground-based testing of most hot plume flow-fields relevant to attitude and orbit control is not feasible, it is necessary to compute these plumes by appropriate numerical methods. The only method today that is, in principle, capable of accurately and efficiently computing engineering scale hypersonic, rarefied flow in three dimensions is Direct Simulation Monte Carlo (DSMC). Confidence in the results of such calculations is much increased if they compare favourably to experimental data. The DLR Göttingen High-Vacuum Plume Test Facility for Chemical Thrusters (STG-CT) uniquely permits studying free plume expansion under space-like vacuum conditions. Steady-state cold gas plumes are especially suited for code validation and a number of free plume expansions from various sources has been studied at STGCT. The standard instrument in this case is an orifice-type impact pressure probe also known as Patterson probe. One powerful method to compare measured and computed data is to reconstruct the probe signal from the computed flow conditions at the probe location. We outline how to account for the particular probe reaction in the post-processing of the numerical solution, and show that only by doing so, a quantitative comparison of numerical to experimental data is permissible.