Techniques for Estimating Rotational and Vibrational Temperature in Nitrogen Arcjet Flow

Abstract

Molecular nitrogen and molecular nitrogen ion spectra are used to infer vibrational and rotational temperatures in an arcjet sbock layer under the assumption of Boltzmann populations. Various techniques correlate spectral features with temperatures, among which are determining intensity integrals and forming ratios that are then correlated with rotational and vibrational temperatures. Sensitivity factors, determined by correlating these ratios with temperature, are indicators of the potential accuracy of different spectrum regions for determining temperature. In another technique, least-squares fits of measured spectra are made to fit temperature-dependent computed spectra, including global fits to computed spectra as a function of temperature or fits to vibrational-level basis spectra. Technique accuracy is described and precision improved by combining the results of several techniques. When results from the various techniques are combined, overall temperature determination accuracy at a single point in an arcjet shock layer is about ±4% for vibrational temperature and ±10% for rotational temperature.