Flow visualization of aircraft in flight by means of Background Oriented Schlieren using Celestial Objects

The Background Oriented Schlieren using Celestial Objects series of flights was undertaken in the spring of 2016 at the National Aeronautics and Space Administration Armstrong Flight Research Center to further develop and improve a flow visualization technique which can be performed from the ground upon flying aircraft. Improved hardware and imaging techniques from previous schlieren tests were investigated. A United States Air Force T-38C and NASA B200 King Air aircraft were imaged eclipsing the sun at ranges varying from 2 to 6 nautical miles, at subsonic and supersonic speeds. Images were postprocessed using the Background Oriented Schlieren technique with optical flow algorithms to reveal both subsonic and supersonic flow features around the aircraft. The resulting imaging hardware and techniques demonstrated its applicability as a mature instrumentation system for performing flow visualization on vehicles in flight.