Simultaneous local jitter, 2-D wavefronts and accelerometer measurements were performed in the flow over a flat-window turret at Mach numbers between 0.3 and 0.4 along a centerplane with a viewing angle varying between 90 and 118 degrees. Both local and global jitter imposed on a small-and large-aperture laser beams were measured using positionsensing devices and a high-speed 2-D wavefront sensor. A linear stochastic estimation technique was applied to separate the mechanically-related component of the jitter from the aero-optical component. Spectra of aero-optical jitter for different elevation angles and speeds were calculated and useful scaling laws were proposed. It was shown that aero-optical jitter was due to the presence of both the stationary and traveling aero-optical components. Detailed analysis of the global and the local jitter spectra and the spectral cross-correlation between them at different speeds and viewing angles is presented and discussed in details. Additionally, PIV system was used to measure the flow field over the flat window, simultaneously with the aero-optical jitter measurements.
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=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.
The optical environment around both a hemisphere-on-cylinder turret and a hemisphereonly turret with flat and conformal windows was characterized at both subsonic and transonic speeds. Data was taken from Mach 0.4 to 0.65 at altitudes from 15,000 ft to 30,000 ft to analyze scaling laws, with a focus on Mach numbers of 0.5 and 0.65. A 25 kHz Shack-Hartmann wavefront sensor was used to measure the optical aberrations around the turret. Data were primarily collected while the two planes slewed by, giving statistics at several azimuthal/elevation angles with additional data taken at fixed angles. Additionally, dynamics of a local shock appearing on the conformal-window turret at the transonic Mach number are presented and discussed.
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