Aero-Optic Calculations of A Spherical Turret at Transonic Flow Eran Arad , Mickey Weidenfeld Aeronautical Systems, RAFAEL Ltd,Haifa ISRAEL 3102102 Flow over a flat-window spherical turret at transonic flow conditions is simulated. An advanced LES method is used for flow simulation. Optical wavefront distortions are real- ized through imaging on an otherwise diffraction limited system. Visual and quantitative representations of the distorted signal are evaluated through the systems’ PSF and MTF functions. Simulation results were validated against well established experiment database of cylinder-hemisphere turret at subsonic flow. At Mach number 0.81, a backward looking configuration faces similar yet amplified wake induced distortions than those produced in subsonic regime. Noteworthy are the forward-looking window results, where an incident planar wavefront propagates through supersonic region and a buffeting shockwave, resulting in a double-image. Shockwave buffeting occurs also beyond the shear layer, in backward- looking configurations, inducing further optical distortions. Analysis of these phenomena together with preliminary evaluation of control technique, designed to mitigate the signal degradation, are reported in the current paper. Nomenclature D Hemisphere diameter f Focal length k Turbulent kinetic energy Mach Mach number MTF Modulation transfer function n Index of refraction (defined in equation 1) OPD Optical Path Difference (defined in equation 4) OPL Optical Path Length (defined in equation 3 ) PSF Point Spread Function Re D Reynolds number based on hemisphere diameter U ∞ Free-stream velocity W Optical window diameter x,y,z Ordinates in main-flow direction, wall-normal and lateral direction, accordingly λ Light wave length Δy + Wall-nondimensional mesh size Δy + = ΔywU∞ ν ρ Flow density ρ SL Reference flow density at sea level I. Introduction T he use of accurate airborne optical systems has become abundant in the last decade, with constantly rising challenges of resolution and range. A severe obstacle in the development of these systems is the close range aero-optical phenomenon. The requirement for a large field-of-regard imposes the use of bluff- body turrets. The flow field over such bluff bodies at flight is turbulent and complex and may cause severe optical aberrations at even low subsonic Mach numbers, as shown by Gorodeyv et al. 1 Density fluctuations in Head, CFD Group Senior Research Engineer 1 of 15 American Institute of Aeronautics and Astronautics