Numerical investigation of aero-optical effects of flow past a flat-windowed cylindrical turret.

Improved delayed detached eddy simulation is performed to investigate aero-optical distortions induced by Mach 0.5 flow over a cylindrical turret with a flat window at a Reynolds number of Re = 5.9 × 105 based on the turret radius. Optical wave-front distortions and associated far-field intensities at elevation angles of 90°, 100°, and 120° are calculated using the geometric ray-tracing method and Fourier optics theory, respectively. The time-averaged properties of the flow fields and the optical distortions are compared with the experimental results, and reasonable agreements are obtained. It is shown that large-scale coherent structures significantly increase the optical distortions and, consequently, degrade the optical performance in terms of the far-field intensity level, while the optical effects of the attached turbulent boundary layers and separation bubbles are trivial and negligible. Very little difference is observed in both instantaneous and statistical optical results calculated with and without defocus and astigmatism components, indicating the adequacy of the removing piston and tilt components for aiding in the design of adaptive optical systems. Both co-flow and blowing jet fluid control methods are introduced with a steady mass flow to alleviate wave-front distortions, and preliminary simulations demonstrate the practicability of these fluid control methods in suppressing the optical distortions. It is shown that both the active control methods are competent to reduce the overall wave-front root-mean-square of the optical path difference. [ABSTRACT FROM AUTHOR]