Nitrogen molecular radiation in hypersonic expanding flow

This study investigates nitrogen molecular radiation in hypersonic expanding flow around a two-dimensional model. Experiments were conducted using the JF-14 shock tunnel in shock tube mode, generating a 3.25 km/s shock wave to create the required flow. A blunt model with a 25-mm nose radius was used to generate the expanding flow. Spatially resolved visible spectra were measured around the model's shoulder. Numerical simulations were then conducted to analyze flow properties and spectral distributions. The results show that the N2 first positive system dominates emissions in the 500–750 nm range. The spectral profiles matched well between experiment and simulation, but predicted intensities were 3–4 times higher, likely due to an overestimation of the excited state density in the model. A detected spectral line near 520 nm, close to the wall, suggests that the predissociation may have been underestimated. This work extends experimental data on hypersonic expanding flow, contributing to an improved understanding of radiation in such flows.