Numerical study on the flow and noise control mechanisms of a forced rotating cylinder

This numerical study proposes an active control method aiming to suppress aerodynamic noise from bluff bodies by employing a forced rotating cylinder and investigates its noise reduction effects and mechanisms. A three-dimensional large eddy simulation combined with the Ffowcs William-Hawkings equation was adopted to study the influence of different rotation ratios on the aerodynamic and aeroacoustic characteristics of a cylinder at a Reynolds number of 4.7 x 104, and to elucidate the primary mechanisms by which cylinder rotation reduces aerodynamic noise. The numerical method is validated through a comparison with previous numerical and experimental results of both flow field and far-field noise. The present numerical results indicate that cylinder rotation can not only effectively reduce aerodynamic drag but also significantly suppress aerodynamic noise across the entire frequency range, including vortex-shedding tonal noise and broadband noise. Two primary mechanisms of flow and noise control by the rotating cylinder are revealed within different ranges of rotation ratio. One mechanism stabilizes the shear layer, thereby suppressing vortex shedding. The other mechanism attenuates the Kelvin- Helmholtz instability on the upper side of the cylinder, leading to a transition into laminar flow which inhibits the formation of large-scale coherent turbulent structures.