If an optical signal were to travel through a hypersonic flow field, the type of high-speed flow analysis required to perform reliable assessments of sensor performance is unclear. In the present study, numerical simulations are utilized to perform implicit large eddy computations of a Mach 4 flow over an adiabatic flat plate. The simulations are run with and without thermochemistry models to determine the effects thermochemical nonequilibrium has on optical distortion. The higher fidelity simulation method of accounting for thermochemical nonequilibrium produces less variation in optical path difference (OPD) across the sensor aperture. The root mean square average of OPD is significantly smaller for the real gas simulation when compared to a perfect gas. These differences in OPD occur because nonequilibrium energy exchanges act to damp out turbulent fluctuations. It is, therefore, necessary to include these physical flow effects in optical assessments to obtain an accurate description of the aero-optic distortions.
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