Effect of the incidence angle of the flow on the acoustic dipolar radiation of rectangular cylinders

Abstract

This study focuses on the noise produced by cylinder-flow interactions. The aerodynamic noise is established when the instabilities in the shear layer lead to periodic vortex shedding. This results in a tonal noise called "aeolian tone". For a rectangular cylinder with no incidence, the sources of noise are located along the spanwise direction. They have a dipolar directivity, orthogonal to the flow. However, when the incidence of the flow varies, the orientation of the dipoles changes. This phenomenon is investigated experimentally in the test section of an anechoic wind-tunnel, with an array of microphones placed orthogonally to the cylinder. The rectangular cylinders studied have two different aspect ratios: AR=1 and AR=2, for Reynolds numbers between 2 000 and 23 000. A beamformingbased method is used to recover the dipolar angles from the microphones data. For the two cylinders, the dipole tilts similarly when changing the flow incidence angle. These results confirm numerical predictions of the sound directivity based on Curle's solution, for a compact source using the drag and lift force fluctuations.