Investigation on the flow and aerodynamic noise characteristics of circular cylinders with slit structures

Based on the delayed detached-eddy simulation model and acoustic analogy method, this study numerically investigates the flow and aeroacoustic characteristics of smooth and slit circular cylinders at a Reynolds number of Re = 6 × 104. The numerical results of aerodynamic noise are validated against anechoic wind-tunnel measurements. The introduction of slits allows high-pressure flow to penetrate the wake and form an internal mixing layer between the through-jet and the recirculation bubble. This additional shear interaction weakens the coupling between the upper and lower separated shear layers, suppresses the formation of a regular Kármán vortex street, and greatly reduces the fluctuations of lift and drag. As the slit width increases from d/D = 0.05 to 0.15, the wake transitions from periodic vortex shedding dominated by a single frequency to a multi-scale broadband turbulent pattern, accompanied by a slight upward shift in the dominant Strouhal number and a noticeably decrease in modal energy. Reduced-order modeling analyses reveal that the coherent large-scale vortices in the slit-cylinder wake are fragmented, with energy redistributed to small scales, which is rapidly dissipated in the near wake. The slit-cylinder cases exhibit noise reductions of 18–28 dB compared with the smooth cylinder, with the pronounced suppression for d/D ≈ 0.10–0.15. This suggests that slit-cylinder configurations can effectively weaken regular vortex shedding and associated unsteady aerodynamic loading, redistribute wake energy and reduce dipole-type aerodynamic noise.