The aeroacoustics of finite wall-mounted square cylinders

• Published in: Journal of fluid mechanics Vol. 832; pp. 287 - 328
• Main Authors: Porteous, Ric, Moreau, Danielle J., Doolan, Con J.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.12.2017
• Subjects: Acoustic noise; Aeroacoustics; Aerodynamics; Aspect ratio; Boundary layer; Boundary layers; Computational fluid dynamics; Cylinders; Downwash; Filaments; Flow structures; Fluid flow; Fluid mechanics; Fluids; Fourier transforms; Inclination; Noise; Pressure distribution; Pressure gradients; Ratios; Reynolds number; Shedding; Studies; Thickness; Vortex filaments; Vortices; Width; Wind tunnels; aeroacoustics; vortex shedding
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2017.682

This paper presents the results of an experimental study that relates the flow structures in the wake of a square finite wall-mounted cylinder with the radiated noise. Acoustic and hot-wire measurements were taken in an anechoic wind tunnel. The cylinder was immersed in a near-zero-pressure gradient boundary layer whose thickness was 130 % of the cylinder width, $W$ . Aspect ratios were in the range $0.29\leqslant L/W\leqslant 22.9$ (where $L$ is the cylinder span), and the Reynolds number, based on width, was $1.4\times 10^{4}$ . Four shedding regimes were identified, namely R0 ( $L/W<2$ ), RI ( $2<L/W<10$ ), RII ( $10<L/W<18$ ) and RIII ( $L/W>18$ ), with each shedding regime displaying an additional acoustic tone as the aspect ratio was increased. At low aspect ratios (R0 and RI), downwash dominated the wake, creating a highly three-dimensional shedding environment with maximum downwash at $L/W\approx 7$ . Looping vortex structures were visualised using a phase eduction technique. The principal core of the loops generated the most noise perpendicular to the cylinder. For higher aspect ratios in RII and RIII, the main noise producing structures consisted of a series of inclined vortex filaments, where the angle of inclination varied between vortex cells.