The structure of an expanding hydrogen arcjet plasma

Abstract

The structure of an expanding low-power hydrogen arcjet plasma is investigated through probe-based measurements of impact pressure and mass flux. Comparisons are made to direct simulation Monte Carlo models (DSMC) of the nonignited flow (cold flow) and continuum magnetohydrodynamic (MHD) models of the arc-heated flow. While general agreement with previous spectroscopic data and DSMC calculations are obtained, the cold flow impact pressures are shown to exhibit features that may be due to probe–flow interactions and rarefied gas effects. The ability to identify shocks in the plume, predicted by the DSMC model and previously observed by Raman spectroscopy, shows that the cold flow probes were capable of resolving major flow features. The impact pressure measurements of arc-heated flow also agree quite well with the results calculated from the MHD model, and it is demonstrated that integrated thrust densities derived from impact pressure measurements are in agreement with direct measurements of thrust using an inverted pendulum thrust stand. Cold flow mass flux measurements appear to agree well with the DSMC model in the core portion of the flow. Using velocity and temperature data obtained from previous laser-induced fluorescence measurements; density, pressure, and thrust profiles were derived from the measured mass flux profiles. The density profile indicates that the dissociation fraction at the exit plane was within the uncertainty of the only direct spectroscopic molecular hydrogen density measurements available in the literature.