Impact of porous coating on wake and acoustic characteristics of wall-mounted circular cylinders with various aspect ratios

Abstract This paper describes a numerical investigation to characterize the impact of porous coating on wake dynamics and radiated noise of a finite wall-mounted circular cylinder (FWCC). The aspect ratios investigated in the current work are 0.5 ≤ A R ≤ 24 at a Reynolds number of R e D = 3.2 × 10 4 . According to the numerical results, there is a correlation between the control effect of porous coating and aspect ratios, and three main regimes are identified, namely RI ( A R < 3.5 ), RII ( 3.5 ≤ A R < 10.4 ), and RIII ( A R ≥ 10.4 ). At low aspect ratios (RI), the downwash flow of solid FWCCs dominates the entire near wake region, leading to the wake behavior exhibiting symmetrical arch vortex shedding, and far-field noise exhibits both low and broadband characteristics. Although the porous coating does not alter the original flow pattern and broadband noise characteristics, it dose weaken the strength of the downwash flow and the aerodynamic noise is decreased by at least 2.1 dB. At transitional aspect ratios (RII), the downwash flow behind solid FWCCs continues to affects the wake structure, and the acoustic spectra exhibit a low-amplitude peak. In contrast, the porous coating facilitates the formation of Kármán-type vortex structures and diminishes the drag loss caused by downwash flow, which is detrimental to drag and noise reduction. For higher aspect ratios in RIII, the Kármán-type vortex structures present in the wake of solid FWCCs cause the generation of tonal noise, and the effect of porous coating on wake dynamics and radiated noise is similar to that of an infinite-length circular cylinder, and the aerodynamic noise decreased by at least 4.1 dB in this regime. Furthermore, the porous coating demonstrates improved performance in drag and noise reduction at higher aspect ratios.