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. Acoustic measurements have been taken using a flat plate with both sharp and serrated trailing edges in an anechoic wind tunnel. Trailing-edge serrations are found to achieve reductions of up to 13 dB in the narrowband noise levels, and this is mainly due to attenuation of vortex shedding at the trailing edge. Velocity data have also been measured in the very-near trailing-edge wake using hot-wire anemometry, and these data are related to the far-field noise measurements to give insight into the trailing-edge serration noise-reduction mechanism. The results show that, for this particular configuration, the noise-reduction mechanism of trailing-edge serrations is dominated by their influence on the hydrodynamic field at the source location. Therefore, the assumption that the turbulent field is unaffected by the serrations is not valid and explains why theory is not able to explain experimental observations.