Shock-related effects on aero-optical environment for hemisphere-on-cylinder turrets at transonic speeds

The aero-optical environment around a hemisphere-on-cylinder turret with both flat and conformal windows was studied experimentally in flight using the Airborne Aero-Optical Laboratory-Transonic for a range of subsonic and transonic Mach numbers between 0.5 and 0.8. Above M=0.6, the local shock appeared near the top of the turret, causing additional aero-optical distortions at side-looking angles. Using time-resolved wavefronts, instantaneous shock locations were extracted and analyzed. The mean shock location was found to be near a viewing angle, α=80  deg for both window types at M=0.7 and 0.8. For M=0.8, the shock has a single frequency peak at St_D=0.15, the same as for the unsteady separation line, indicating a lock-in mechanism between the shock and the separated wake region. Analysis of aero-optical distortions in the wake indicated that the wake dynamics were beginning to be affected by the shock only at high transonic speed of M=0.8 for the conformal-window turret.