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

Abstract

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.

Experimental studies of aero-optical properties of subsonic turbulent boundary layers

“…The relation between the global and the local tilt was derived by DeLucca et al (2012) and it was shown that the removal of the global tilt works as a high-pass filter on the local deflection angle, with the transfer function, G A (z) = [3 sin(πz) − 3πz cos(πz)](Colour online) (a) Streamwise deflection-angle amplitude spectra computed from 1-D wavefront data for different apertures, compared with the Malley probe deflection-angle amplitude spectrum. (b) Streamwise deflection-angle amplitude spectra computed from 1-D wavefront data for different apertures, corrected for aperture effects, the corrected Malley probe deflection-angle amplitude spectrum and the empirical fit, given by (4.2).…”

Aperture Effects on Aero-Optical Distortions Caused by Subsonic Boundary Layers

“…Recent careful comparisons between timeresolved 2-D wavefront measurements and 1-D Malley probe wavefront measurements have shown that there is significant low-frequency corruption in the Malley probe spectra from various sources [13]. It was shown in [13] that less-corrupted experimental measurements of the low-frequency (below-peak) deflection angle spectra can be obtained from time-resolved 2-D wavefront measurements, once correction for a finite-aperture size from [17] has been applied. This correction is necessary since wavefront tip/tilt removal has been shown to act as a high-pass filter…”

“…, where = [3 sin( ) − 3 cos( )] /( ) 3 , and = 1.2( / ) [17]. A comparison of Malley-Probe spectra and aperture-corrected wavefront spectra is shown in Figure 6.…”

The Comparison of Unsteady Pressure Field over Flat- and Conformal-Window Turrets using Pressure Sensitive Paint

“…While the turret vibrational response depends on an internal structure, an unsteady pressure field depends only on the turret geometry Gordeyev at al AIAA-2013-XXXX 2 American Institute of Aeronautics and Astronautics and the incoming Mach number. In addition, unsteady pressure fluctuations on the surface of the turret are directly related to the turbulent structures, causing aero-optical global jitter and higher-order aberrations [10].…”