Determination of Temperature Profiles in the Plenum Region of the NASA IHF Arc Jet Facility from Emission Spectroscopic Measurements

摘要

Emission spectroscopy data taken in the plenum of the NASA Ames 60 MW Interaction Heating Facility (IHF) were analyzed to validate best practices for determining an inflow condition for CFD simulation of the arc-jet flow. Previously, data analysis was performed through a comparison of the experimental spectra with simulated ones based on the existing CFD simulation. In this work, an equilibrium chemistry data base is built and used to generate a spectral database for relevant temperatures and pressures. Through iteration of plasma conditions matching the experimental data at different offset positions, radial profiles of equilibrium temperatures were obtained characterizing the local specific enthalpy in the plenum. This method has the advantage of being independent from any modeling assumption (except the justifiable assumption of equilibrium conditions). In a first step, the temperature profiles were iterated manually. For this purpose, the plenum was divided in a number of rings with constant compositions and temperatures, according to the number of lines of sight available from the experimental data. In parallel, a method for automatically fitting these conditions through Fortran code was developed. Both methods were found to agree and were able to fit the measured data. In comparison to the CFD solution, the temperature profiles obtained in this work showed significantly higher temperatures at the center line of the plenum, but lower values close to the wall. Therefore, the plasma beam seems to form a hot core region with a distinct temperature profile. Furthermore, these preliminary results indicate that current practices of assuming a swirl flow with reduced static pressures at the center line of the plenum seems to be inappropriate. Future work will include a statistic analysis of repeated measurements of the same plasma condition, as well as parametric investigations of possible pressure distributions inside the plenum region and continuous temperature distributions along the plenum radius.