Numerical study on passive flow and noise control of finite wall-mounted cylinder with porous coatings

This study systematically investigates the control mechanism of porous media coating on flow characteristics and aerodynamic noise of a finite wall-mounted cylinder (aspect ratio AR = 6) at a Reynolds number Re = 50 000 (based on cylinder diameter), using large eddy simulation coupled with the Ffowcs Williams–Hawkings acoustic model. The study focuses on analyzing the effects of different spatial distributions of porous materials (full axial coverage, free-end partial coverage, near-wall partial coverage, mid-cylinder coverage, and combined free-end/near-wall coverage) on the three-dimensional separated flow field. Results demonstrate that the permeability of porous media can delay boundary layer separation, disrupt the coherence of shear layer vortical structures, and modify Reynolds stress distribution and anisotropy characteristics in the wake region. Consequently, large-scale Kármán vortices break down into smaller turbulent structures, enhancing wake energy dissipation and reducing overall flow instability. For free-end coverage, porous media effectively weaken tip vortex entrainment and significantly reduce downwash intensity. For near-wall coverage, they alleviate horseshoe vortex separation and reconstruct wall boundary layer dynamics. The full axial coverage case (300° circumferential coverage angle) demonstrates optimal control performance, achieving synergistic optimization of multi-scale interactions between free-end and near-wall regions. This effectively improves both flow field structure and acoustic source characteristics, resulting in a 29.5% reduction in mean drag coefficient and 46.6% attenuation of dominant frequency sound pressure level. This research provides significant theoretical support for flow control design of bluff bodies in engineering applications.