Abstract:

This paper presents the results of an experimental investigation exploring the noise reduction potential of sawtooth trailing edge serrations on a flat plate at low-to-moderate Reynolds number (1.6e5 < Rec < 4.2e5). Acoustic and aerodynamic measurements have been taken using a flat plate with both sharp and serrated trailing edges in the anechoic wind tunnel at the University of Adelaide. Trailing edge serrations are found to achieve up to 13 dB of attenuation in the narrowband noise levels without modifying the directivity of the radiated noise. The noise reduction achieved with trailing edge serrations is found to be dependent on their geometrical wavelength and Strouhal number, St = fd/U, where f is frequency, d is boundary layer thickness and U is free-stream velocity. Far-field acoustic data are compared with theoretical noise reduction predictions showing that significant differences exist between measurements and theory. Velocity data measured in the very near trailing edge wake with hot-wire anemometry are related to the far-field noise measurements to give insight into the trailing edge serration noise reduction mechanism. The results suggest that for this particular configuration, the noise reduction capability of trailing edge serrations is related to their influence on the hydrodynamic field at the source location.