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Boundary-layer instability noise on aerofoils

Nash, Emma C., Lowson, Martin V. and McAlpine, Alan (1999) Boundary-layer instability noise on aerofoils Journal of Fluid Mechanics, 382, pp. 27-61. (doi:10.1017/S002211209800367X).

Record type: Article

Abstract

An experimental and theoretical investigation has been carried out to understand the tonal noise generation mechanism on aerofoils at moderate Reynolds number. Experiments were conducted on a NACA0012 aerofoil section in a low-turbulence closed working section wind tunnel. Narrow band acoustic tones were observed up to 40 dB above background noise. The ladder structure of these tones was eliminated by modifying the tunnel to approximate to anechoic conditions. High-resolution flow velocity measurements have been made with a three-component laser-Doppler anemometer (LDA) which have revealed the presence of strongly amplified boundary-layer instabilities in a region of separated shear flow just upstream of the pressure surface trailing edge, which match the frequency of the acoustic tones. Flow visualization experiments have shown these instabilities to roll up to form a regular Kármán-type vortex street.

A new mechanism for tonal noise generation has been proposed, based on the growth of Tollmien–Schlichting (T–S) instability waves strongly amplified by inflectional profiles in the separating laminar shear layer on the pressure surface of the aerofoil. The growth of fixed frequency, spatially growing boundary-layer instability waves propagating over the aerofoil pressure surface has been calculated using experimentally obtained boundary-layer characteristics. The effect of boundary-layer separation has been incorporated into the model. Frequency selection and prediction of T–S waves are in remarkably good agreement with experimental data.

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Published date: March 1999

Identifiers

Local EPrints ID: 147671
URI: http://eprints.soton.ac.uk/id/eprint/147671
ISSN: 0022-1120
PURE UUID: a03e48f6-cda4-452e-b958-30707560f614
ORCID for Alan McAlpine: ORCID iD orcid.org/0000-0003-4189-2167

Catalogue record

Date deposited: 17 Jun 2010 14:04
Last modified: 18 Jul 2017 19:33

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