Emission Spectroscopy Through Converging–Diverging Nozzle of Hypersonic Arcjet Tunnel

In this study, quantitative emission spectroscopy measurements of a nonequilibrium expanding flow were taken along the Mach 6 nozzle of a pulsed arcjet wind tunnel, operated with pure nitrogen ([Formula: see text]) flow. The nozzle is equipped with optical access points located at eight axial stations along the flow path, from the plenum chamber to the nozzle exit. High resolution spectra were collected in the near-UV (275–475 nm) and near-IR (730–1000 nm) regions to detect emissions from molecular and atomic nitrogen, respectively. In the near-UV, spectra from both the first negative system of [Formula: see text] and the second positive system of [Formula: see text] were analyzed using a line-by-line radiation code. Rotational, vibrational, and ionization temperatures, along with number densities, were determined assuming a two-temperature nonequilibrium model. The collection of molecular spectra was restricted to the two most upstream positions (the plenum chamber and the sonic throat), where the signal-to-noise ratio was sufficient for quantitative analysis. Atomic emission spectra in the near-IR were collected at all seven longitudinal stations of the nozzle, as well as the plenum chamber, allowing absolute population measurement for several excited states of atomic nitrogen.