The University of Southampton
University of Southampton Institutional Repository

Estimation of the far-field directivity of broadband aeroengine fan noise using an in-duct axial microphone array

Estimation of the far-field directivity of broadband aeroengine fan noise using an in-duct axial microphone array
Estimation of the far-field directivity of broadband aeroengine fan noise using an in-duct axial microphone array
This paper presents a measurement technique for estimating the far-field directivity of the sound radiated from a duct using measurements of acoustic 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. Transfer functions for practical cases concerning aeroengine exhausts are also presented. The transfer function is shown to be insensitive to the mode-amplitude distribution inside the duct, and hence can be used to predict the directivity in practice where the noise source distribution is unknown. The technique is then validated using a no-flow facility, and is shown to be able to predict variations in the far-field directivity pattern and also estimate the far-field sound pressure levels to within 2 dB. It is suggested that the proposed technique will be especially useful for fan rig experiments, where direct measurement of directivity, for example by use of an anechoic chamber, is impossible.
0022-460X
3940-3957
Lowis, C.R.
051751e2-c67f-4cd5-bc27-2237f7b0a33e
Joseph, P.F.
9c30491e-8464-4c9a-8723-2abc62bdf75d
Kempton, A.J.
08276625-e640-431b-8dd3-1598fe5ec722
Lowis, C.R.
051751e2-c67f-4cd5-bc27-2237f7b0a33e
Joseph, P.F.
9c30491e-8464-4c9a-8723-2abc62bdf75d
Kempton, A.J.
08276625-e640-431b-8dd3-1598fe5ec722

Lowis, C.R., Joseph, P.F. and Kempton, A.J. (2010) Estimation of the far-field directivity of broadband aeroengine fan noise using an in-duct axial microphone array. Journal of Sound and Vibration, 329 (19), 3940-3957. (doi:10.1016/j.jsv.2010.03.021).

Record type: Article

Abstract

This paper presents a measurement technique for estimating the far-field directivity of the sound radiated from a duct using measurements of acoustic 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. Transfer functions for practical cases concerning aeroengine exhausts are also presented. The transfer function is shown to be insensitive to the mode-amplitude distribution inside the duct, and hence can be used to predict the directivity in practice where the noise source distribution is unknown. The technique is then validated using a no-flow facility, and is shown to be able to predict variations in the far-field directivity pattern and also estimate the far-field sound pressure levels to within 2 dB. It is suggested that the proposed technique will be especially useful for fan rig experiments, where direct measurement of directivity, for example by use of an anechoic chamber, is impossible.

This record has no associated files available for download.

More information

Published date: 13 September 2010
Organisations: Fluid Dynamics & Acoustics Group

Identifiers

Local EPrints ID: 154059
URI: http://eprints.soton.ac.uk/id/eprint/154059
ISSN: 0022-460X
PURE UUID: 63fca337-6edd-4c8c-af73-8ae0b32e7bdb

Catalogue record

Date deposited: 24 May 2010 10:27
Last modified: 14 Mar 2024 01:32

Export record

Altmetrics

Contributors

Author: C.R. Lowis
Author: P.F. Joseph
Author: A.J. Kempton

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×