Flight Measurements of the Aero-Optical Environment Around a Flat-Windowed Turret

This paper discusses the aero-optical environment for a flat-window hemisphere-on-cylinder turret over a wide range of viewing angles during flight tests in the Airborne Aero-Optics Laboratory. Aero-optical aberrations around the turret were measured using a high-speed Shack-Hartmann wave-front sensor providing an extensive aero-optical mapping. The primary data were acquired at Mach 0.5 at an altitude of 15,000 ft, with a subset of the data collected at Mach 0.4 for verification of scaling relationships. Data were acquired holding the relative position between two aircrafts constant. Additional data sets were acquired allowing two aircrafts to change their relative positions so that stewing data could be acquired; this provided statistical data over a large range of viewing angles between looking-forward to looking-back angles. Results were analyzed, and the aero-optical contribution from different flow features over the turret was identified and discussed. Cross-correlation functions and convective speed were also computed for some viewing angles and compared with other experiments. The flight-test data were also compared to wind-tunnel measurements using the identical turret.