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An in-duct beamformer for the estimation of far-field directivity

An in-duct beamformer for the estimation of far-field directivity
An in-duct beamformer for the estimation of far-field directivity
This paper presents a measurement technique for estimating the far-field directivity of the sound radiated from a duct using measurements of pressure made inside the duct. The technique is restricted to broadband, multi-mode sound fields whose directivity patterns are axi-symmetric, and whose modes are mutually uncorrelated. The technique uses a transfer function to relate the output from an in-duct axial beamformer to measurements of the far-field polar directivity. A transfer function for a hollow cylindrical duct with no flow is derived, and investigated in detail. The transfer function is shown to be insensitive to the mode-amplitude distribution inside the duct, and hence a predicted transfer function can be used to predict the directivity in practice where the noise source distribution is unknown. It is suggested that the proposed technique will be especially useful for fan rig experiements, where direct measurement of directivity, for example by use of an anechoic chamber, is impossible. The technique is validated using a no-flow experiment.
Lowis, C.
42fc49d5-4244-43d4-a062-9c0bae92c2d1
Joseph, P.F.
9c30491e-8464-4c9a-8723-2abc62bdf75d
Kempton, A.
7bd2386b-d23f-4d0e-b996-19978b553e7a
Lowis, C.
42fc49d5-4244-43d4-a062-9c0bae92c2d1
Joseph, P.F.
9c30491e-8464-4c9a-8723-2abc62bdf75d
Kempton, A.
7bd2386b-d23f-4d0e-b996-19978b553e7a

Lowis, C., Joseph, P.F. and Kempton, A. (2008) An in-duct beamformer for the estimation of far-field directivity. Proceedings of the 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference). 05 - 07 May 2008. 19 pp .

Record type: Conference or Workshop Item (Paper)

Abstract

This paper presents a measurement technique for estimating the far-field directivity of the sound radiated from a duct using measurements of pressure made inside the duct. The technique is restricted to broadband, multi-mode sound fields whose directivity patterns are axi-symmetric, and whose modes are mutually uncorrelated. The technique uses a transfer function to relate the output from an in-duct axial beamformer to measurements of the far-field polar directivity. A transfer function for a hollow cylindrical duct with no flow is derived, and investigated in detail. The transfer function is shown to be insensitive to the mode-amplitude distribution inside the duct, and hence a predicted transfer function can be used to predict the directivity in practice where the noise source distribution is unknown. It is suggested that the proposed technique will be especially useful for fan rig experiements, where direct measurement of directivity, for example by use of an anechoic chamber, is impossible. The technique is validated using a no-flow experiment.

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More information

Published date: May 2008
Additional Information: Paper Number: AIAA 2008-2859
Venue - Dates: Proceedings of the 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), 2008-05-05 - 2008-05-07

Identifiers

Local EPrints ID: 57782
URI: https://eprints.soton.ac.uk/id/eprint/57782
PURE UUID: 82a20350-74bd-48ea-a54f-313d5e71955e

Catalogue record

Date deposited: 20 Aug 2008
Last modified: 13 Mar 2019 20:33

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