Polarizability and Refractivity of Gases in Thermochemical Nonequilibrium

Abstract

The physics of hypersonic flight is challenging due to the high-temperature environment and presence of chemical and vibrational nonequilibrium. Hypersonic flow over a blunt wedge body is studied for different chemical species, each individually present in air. A semi-classical quantum mechanical model, which calculates the polarizability as a function of the translational and vibrational temperature, is used. The temperature fields from simulated nitrogen, oxygen, and argon flows are used to find the polarizability and refractive index fields. Experiments are performed in the Hypervelocity Expansion Tunnel at various Mach numbers and flight conditions corresponding to altitudes ranging from 35,000 to 45,000 feet. A Michelson interferometer with significant reference mirror tilt is used to generate static interferograms to measure the phase difference. The resultant refractive index fields are compared directly to the model to analyze thermochemical nonequilibrium effects. An uncertainty analysis of the experimental data was performed to under-stand any observed deviations from the model.