The Study of Aero-Optical and Mechanical Jitter for Flat Window Turrets

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 smalland 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.