Tonal noise from trailing edge serrations at low Reynolds numbers

Abstract

The flow and noise created by trailing edge serrations has been studied experimentally, at low Reynolds number (Rec = 1×105 - 1.3×105, based on chord). Wide trailing edge serrations with a wavelength () to amplitude (2h) ratio of s/h = 0.6 were found to reduce the overall sound pressure level by up to 11 dB. In contrast, narrower trailing edge serrations with s/h = 0.2 produce high amplitude tonal noise and an increase in the overall sound pressure level of up to 4 dB. Unsteady flow data in near the trailing edge wake show that the narrow serrations are responsible for the formation of intense vortices across the span and this results in the production of high amplitude tonal noise. Wide serrations reduce turbulent velocity fluctuations at low frequencies which explains the lower radiated noise.