Aero-Optical and Flow Measurements Over a Flat-Windowed Turret

An extensive investigation of the aberrating character of flow over a hemisphere-on-cylinder turret with a flat window was performed. Optical distortions over the window were measured using a two-dimensional wave front sensor and a Malley probe. The Malley probe measurements were complemented with simultaneous hot-wire measurements of the velocity field normal to thewindow at several points across its diameter. The tests were run for a fixed elevation for several azimuthal angles over a range ofMach numbers. The results provide the levels of unsteady optical aberration across the window, as well as the local thickness, intensity, and convective speed of the separated flow over the window. Results reveal that the optical distortions grow approximately with the square of the incoming Mach number multiplied by the freestream density, OPDrms M2, as well as with the changing character of the aberrating flow with azimuth angle. Nomenclature Ap = laser beam round aperture diameter Corr = velocity-jitter signal correlation function Efg = time/ensemble averaging procedure F = focal length f = frequency I = far-field point-spread function M = Mach number OPD = optical path difference OPDrms = root mean square of optical path difference R = flat-mirror radius S = jitter signal cross-correlation function s = beams spacing T = block sampling time t = time Uc = convective speed Ufree = freestream speed W = wave front u = streamwise velocity component x, y, z = turret coordinate system , 1, 2 = far-field coordinates = beam displacement 1, 2 = jitter signals = azimuthal angle = laser wavelength = freestream density SL = sea-level density, SL 1:229 kg m3 I.