High resolved Optical Emission Spectroscopy as accurate physics methodology for plasma freestream temperature characterization

In this work the hypersonic plasma flow generated by SCIROCCO hypersonic facility has been experimen-tally characterized as test case, using a high resolved Optical Emission Spectroscopy (OES) during a high enthalpy test campaign. The CIRA methodology to measure roto-translational and NO vibrational temper-atures of a free jet via analyses performed in the Ultra Violet spectral range has been improved and a comparison between experimental data and Computational Fluid Dynamics (CFD) simulations has been carried out. The revised methodology estimates the roto-translational and vibrational temperatures using high definition spectroscopy carried out at conditions of high values of pressure and enthalpy. In particular, attention is mainly focused on the NO emission band at Non-Local Thermal Equilib-rium (NLTE) conditions in the hypersonic flight regime which means equilibrium between the molecular rotational and translational degrees of freedom but not between the roto-translational and vibrational degrees of freedom. Three tests at high enthalpy hypersonic conditions (23.8, 24.0 and 26.0 MJ/kg at a total pressure of about 2.5 bars) have been investigated and experimental data have been compared with numerical simulations in order to verify sensitivity of the method in estimating the small variation in NO roto-translational and vibrational temperatures by changing slightly the total enthalpy fluid-dynamic conditions. The current work presents a high definition spectral method which can be used to determine the temperature of NLTE hypersonic free jets, and may serve as a benchmark in determining the accuracy of various numerical models dedicated to these flow regimes. (c) 2022 Elsevier Ltd. All rights reserved.