Acoustic Beamforming and Holography Measurements of Modified Boundary Layer Trailing-Edge Noise

Abstract

This paper investigates how the trailing-edge noise mechanism is affected by manipulation of the turbulent boundary layer by means of suction and blowing. By manipulating the boundary layer (the noise source) and determining the effect on trailing- edge noise, better understanding of the trailing-ed ge noise generation mechanism can be gained. A 0.5 m chord, 0.585 m span NACA 0012 aerofoil was tested on an acoustically treated open-jet wind tunnel. Changeable plates were used on a hollow trailing-edge to allow suction and blowing manipulation of the boundary layer near the trailing-edge. Suction/blowing was achieved using an industrial va cuum/blower with an inline acoustic silencer to minimize noise contamination due to the vacuum/blower. Acoustic measurements were obtained using a Bruel & Kjaer 60-channel sector-wheel-array suited for both beamforming and acoustic holography measurements. The two acoustic measurement techniques, were used to obtain measurements over the frequency range of interest for trailing-edge noise. Hotwire anemometry was used for aerodynamic measurements of the boundary layer noise source. The results in this pa per detail: 1) the effect on trailing-edge noise of the different trailing-edge plate geometri es 2) the effect on trailing-edge noise of manipulating the boundary layer using suction and blowing 3) the aerodynamic effect of suction and blowing on the boundary layer velocity fluctuations.