Numerical investigation of flow features and aero-optical effects of turrets with different bottom cylinder heights in a transonic flow

Improved delay detached eddy simulation is performed to explore the flow features and aero-optical effects of turrets with different bottom cylinder height at a freestream Mach number Ma = 0.7. Analysis of both the time-averaged and instantaneous flow features demonstrate that the shock motion causes the oscillation of separated shear layer. In flow analysis, two unsteady shock-wake-correlated modes are discerned: the asymmetric shifting mode and the symmetric breathing mode. With the increase of cylinder height, the relative energy of shock gradually increases, which goes from 26% to 59%. The proper orthogonal decomposition analysis yields the single frequency peak for the two dominant modes. The frequency peaks of shifting mode are generally at St_D < 0.23, while the frequency peaks of breathing mode are generally at St_D > 0.26. The dynamic mode decomposition analysis gives range of frequency peak. The frequency peaks of shifting mode are in the range of St_D = 0.11–0.23, and the frequency peaks of breathing mode are in range of St_D = 0.26–0.41. Optical distortion analysis indicates that the distortion calculated in five cases is linked to the breathing mode. When the beam passes through the turbulent wake, it exhibits the high-frequency and high-amplitude characteristics.