Senhao Zhang

The ablation product carbon dioxide (CO2) around the hypersonic vehicle may become an important source of radiation. Accurate simulation of the chemical reaction process between CO2 and air is of great significance for the design of thermal protection systems. A combination of ground experiments and numerical simulations is used in this study to investigate the reaction process of CO2–air mixtures with different proportions behind shock waves with velocities ranging from 3.6 to 4.1 km/s. Flow parameters are simulated based on the two-temperature (2-T) model and the Lee and Park chemical reaction mechanism, and the laser absorption spectroscopy measurements are carried out on the Φ800 mm shock tube at the Chinese Academy of Sciences, Institute of Mechanics, to obtain time-resolved post-shock gas temperatures and partial pressures of CO2 and carbon monoxide (CO). Measurement results indicate that the post-shock temperature is much higher than the equilibrium value when it is close to the shock front and then gradually develops towards equilibrium. The partial pressure of CO2 shows the same trend as temperature. Comparisons between experimental results and calculated results show that the used model can accurately predict the post-shock temperature. When the initial CO2 volume fraction is below 50%, the model underestimates the CO2 dissociation rate, meaning that the actual CO2 content is lower than the calculated value and the CO content is higher. Conversely, when the CO2 volume fraction is greater than or equal to 50%, the prediction of the CO2 dissociation rate tends to be overestimated.

This study investigates the radiative properties of hypersonic carbon dioxide (CO2) expanding flows. Spatially resolved spectral measurements for the expansion region of a two-dimensional model were conducted in the JF14 shock tunnel. Experiments were performed in a shock tube mode, where the shock wave with velocities ranging from 3.37 to 3.88 km/s directly propagates to the test section, forming a stable flow field around the model. Results showed that the radiation emission within the 250–710 nm range is primarily dominated by CO2 chemiluminescence and Schumann–Runge bands of molecular oxygen (O2). The intensity of the Schumann–Runge spectrum was found to be significantly higher than the O2 thermal radiation calculated under the two-temperature (2-T) model, indicating that the O2 excited state (O2(3B)) was overpopulated relative to the Boltzmann distribution in the expansion region. In regions with lower degrees of expansion, the CO2 chemiluminescence intensity was overestimated by about 3 to 6 times, which may be attributed to an overprediction of the atomic oxygen (O) and carbon monoxide (CO) number densities in the current thermochemical model. As the degree of expansion intensified, the CO2 chemiluminescence intensity gradually exceeded the predicted values, suggesting that the expansion process can accelerate the recombination of O and CO, leading to stronger CO2 chemiluminescence. This work enhances the understanding of radiative processes in hypersonic CO2 expanding flow and provides benchmarks for the development of thermochemical and radiative models.

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.