Abstract
Large-eddy simulations are performed for a Mach 0.5 flow over a cylindrical turret with turbulent separation over a flat optical window. Optical wave-front distortions induced by the separated shear layer are calculated based on the computed fluctuating-density field, the Gladstone–Dale relation, and ray tracing. The statistical properties of the flowfield and optical distortions are compared with experimental measurements, and reasonable agreement is obtained. It is found that pressure fluctuations in the separated shear layer are the dominate mechanism of optical distortions. The magnitude and correlation length scales of wave-front distortions increase with streamwise aperture size, and the frequency spectra of distortions exhibit a slope in the inertial subrange of the turbulent flow. Very little difference in the flow and optical statistics is observed at two different Reynolds numbers, indicating Reynolds number insensitivity. The similarities and differences of the aero-optical characteristics of the separated shear layer and the upstream boundary layer are also discussed.
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