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The generation of tonal noise from sawtooth trailing-edge serrations at low Reynolds numbers

Published online by Cambridge University Press:  10 May 2016

D. J. Moreau  and
C. J. Doolan
D. J. Moreau*
Affiliation:
School of Mechanical and Manufacturing Engineering, University of New South Wales, SydneyAustralia
C. J. Doolan
Affiliation:
School of Mechanical and Manufacturing Engineering, University of New South Wales, SydneyAustralia
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Abstract

The flow and noise created by sawtooth trailing-edge serrations has been studied experimentally at a low Reynolds number. Experiments have been performed on a flat-plate model with an elliptical leading edge and an asymmetrically bevelled trailing edge at Reynolds numbers of Rec = 1 × 105–1.3 × 105, based on chord. Wide serrations with a wavelength (λs) to amplitude (2h) ratio of λs/h = 0.6 were found to reduce the overall sound pressure level by up to 11dB. In contrast, narrower serrations with λs/h = 0.2 produce tonal noise and increase the overall noise level by up to 4dB. Intense vortices across the span of the trailing edge with narrow serrations are shown to be the source of tonal noise. Wide serrations reduce turbulent velocity fluctuations at low frequencies which explains the lower radiated noise. The narrow serrations that produce low Reynolds number tonal noise were shown previously to be effective at higher Reynolds numbers (Rec > 2 × 105), demonstrating that care is needed to fully understand the flow field over serrations for all intended operating conditions.

Keywords

Aeroacousticstrailing-edge noisewind tunnel testingaerofoil noise
Type
Research Article
Information
The Aeronautical Journal , Volume 120 , Issue 1228 , June 2016 , pp. 971 - 983
Copyright
Copyright © Royal Aeronautical Society 2016 

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