Reduction of vortex shedding noise from finite, wall-mounted, circular cylinders using porous material

Abstract

The aerodynamic noise generated by a circular cylinder in a cross flow is a classical problem in aeroacoustics, which can be found in various practical applications such as antennas of vehicles, train pantographs and parts of the landing gear of airplanes. The noise is especially disturbing since it contains strong tonal contributions due to the regular vortex shedding at the cylinder. If the cylinders are not two-dimensional, but finite and wall-mounted at one end and free at the other, additional flow phenomena occur at both the tip and the wall junction, which can lead to additional noise contributions. One method to reduce the aerodynamic noise from such cylinders is to cover them with a flow permeable, porous material. The present paper describes an experimental study on the effect of porous covers on the reduction of noise generated by wall mounted, finite, circular cylinders. Three different porous materials were tested. Thereby, special focus was put on the identification of both the optimum position and the optimum extent of the porous cover regarding a maximum noise reduction. The experiments were conducted in an aeroacoustic open jet wind tunnel at subsonic flow speeds, leading to low to moderate Reynolds numbers between 8,000 and 61,000 based on the outer cylinder diameter. It was found that a placement of porous material at the wall end is more efficient in reducing Kármán vortex shedding noise than a placement of porous material at the free end.