Effects of Cavity Geometry and Thermochemistry on Optical Systems in Hypersonic Vehicles

This work investigates the effect of different cavity geometries of optical systems in hypersonic vehicles on optical distortion to characterize the signal quality. Significant distortion affects the vehicle's ability to identify objects of interests and impedes navigation. The impact of including thermochemistry and angle of freestream flow are examined. These effects are studied using the computational fluid dynamics code, US3D, specifically the RANS SA-Catris model and conjugate heat transfer. Three different geometries are examined at a flight condition of Mach 7 at 20 km: a sensor window flush with a flat plate, an open cavity of L/D = 2, and a closed cavity of L/D = 16. The primary two types of distortion included in this work are aero-optical distortion and window deformation. These are evaluated using the Strehl ratio as an image quality metric. Findings suggest that placing the sensor window in cavities result in worse distortion than when flush with the surface of the vehicle. A freestream velocity at an angle 15 degrees emulates a 15 degree ramp, demonstrating that image quality degrades much faster than at 0 degrees. Boresight error is also larger in cavity geometries. The results of this work may provide insight into better optical sensor system design on hypersonic vehicles.