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Sound radiation from a flanged inclined duct

Sound radiation from a flanged inclined duct
Sound radiation from a flanged inclined duct
A simple method to calculate sound radiation from a flanged inclined duct is presented. An inclined annular duct is terminated by a rigid vertical plane. The duct termination is representative of a scarfed exit. The concept of a scarfed duct has been examined in turbofan aero-engines as a means to, potentially, shield a portion of the radiated sound from being transmitted directly to the ground. The sound field inside the annular duct is expressed in terms of spinning modes. Exterior to the duct, the radiated sound field owing to each mode can be expressed in terms of its directivity pattern, which is found by evaluating an appropriate form of Rayleigh's integral. The asymmetry is shown to affect the amplitude of the principal lobe of the directivity pattern, and to alter the proportion of the sound power radiated up or down. The methodology detailed in this article provides a simple engineering approach to investigate the sound radiation for a three-dimensional problem.
0001-4966
3637-3646
McAlpine, Alan
aaf9e771-153d-4100-9e84-de4b14466ed7
Daymond-King, Alex
172c6608-293b-42c8-8c4a-a87265a7b3d3
Kempton, Andrew
08276625-e640-431b-8dd3-1598fe5ec722
McAlpine, Alan
aaf9e771-153d-4100-9e84-de4b14466ed7
Daymond-King, Alex
172c6608-293b-42c8-8c4a-a87265a7b3d3
Kempton, Andrew
08276625-e640-431b-8dd3-1598fe5ec722

McAlpine, Alan, Daymond-King, Alex and Kempton, Andrew (2012) Sound radiation from a flanged inclined duct. Journal of the Acoustical Society of America, 132 (6), 3637-3646. (doi:10.1121/1.4764883).

Record type: Article

Abstract

A simple method to calculate sound radiation from a flanged inclined duct is presented. An inclined annular duct is terminated by a rigid vertical plane. The duct termination is representative of a scarfed exit. The concept of a scarfed duct has been examined in turbofan aero-engines as a means to, potentially, shield a portion of the radiated sound from being transmitted directly to the ground. The sound field inside the annular duct is expressed in terms of spinning modes. Exterior to the duct, the radiated sound field owing to each mode can be expressed in terms of its directivity pattern, which is found by evaluating an appropriate form of Rayleigh's integral. The asymmetry is shown to affect the amplitude of the principal lobe of the directivity pattern, and to alter the proportion of the sound power radiated up or down. The methodology detailed in this article provides a simple engineering approach to investigate the sound radiation for a three-dimensional problem.

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Published date: December 2012
Organisations: Acoustics Group

Identifiers

Local EPrints ID: 346920
URI: http://eprints.soton.ac.uk/id/eprint/346920
ISSN: 0001-4966
PURE UUID: 04d74dce-b34a-4642-ada2-c8a68f9ae4d6
ORCID for Alan McAlpine: ORCID iD orcid.org/0000-0003-4189-2167

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Date deposited: 21 Jan 2013 16:02
Last modified: 15 Mar 2024 03:00

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Contributors

Author: Alan McAlpine ORCID iD
Author: Alex Daymond-King
Author: Andrew Kempton

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