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Acoustic scattering by a spliced turbofan inlet duct liner at supersonic fan speeds

Acoustic scattering by a spliced turbofan inlet duct liner at supersonic fan speeds
Acoustic scattering by a spliced turbofan inlet duct liner at supersonic fan speeds
Fan noise is one of the principal noise sources generated by a turbofan aero-engine. At supersonic fan speeds, fan tones are generated by the “rotor-alone” pressure field. In general, these tones can be well absorbed by an inlet duct acoustic liner, apart from at high supersonic fan speeds. However, in practice inlet duct liners contain acoustically hard longitudinal splices which cause scattering. This leads to acoustic energy being scattered into a range of different azimuthal mode orders, similar to the modal content resulting from rotor–stator interactions. The effectiveness of an inlet duct lining is reduced because acoustic energy is scattered into modes that are poorly absorbed by the liner. In this article, the effect of this acoustic scattering is examined by three-dimensional finite-element simulations of sound transmission in a turbofan inlet duct. Results include predictions of the sound power transmission loss with different splice widths, and at different supersonic fan speeds. These results demonstrate how acoustic scattering by liner splices can adversely affect fan tone noise levels at low supersonic fan speeds, but have little adverse affect on noise levels at high supersonic fan speeds. The potential noise benefit that could be achieved by manufacturing thinner splices is also examined.
0022-460X
911-934
McAlpine, A.
aaf9e771-153d-4100-9e84-de4b14466ed7
Wright, M.C.M.
b7209187-993d-4f18-8003-9f41aaf88abf
McAlpine, A.
aaf9e771-153d-4100-9e84-de4b14466ed7
Wright, M.C.M.
b7209187-993d-4f18-8003-9f41aaf88abf

McAlpine, A. and Wright, M.C.M. (2006) Acoustic scattering by a spliced turbofan inlet duct liner at supersonic fan speeds. Journal of Sound and Vibration, 292 (3-5), 911-934. (doi:10.1016/j.jsv.2005.09.010).

Record type: Article

Abstract

Fan noise is one of the principal noise sources generated by a turbofan aero-engine. At supersonic fan speeds, fan tones are generated by the “rotor-alone” pressure field. In general, these tones can be well absorbed by an inlet duct acoustic liner, apart from at high supersonic fan speeds. However, in practice inlet duct liners contain acoustically hard longitudinal splices which cause scattering. This leads to acoustic energy being scattered into a range of different azimuthal mode orders, similar to the modal content resulting from rotor–stator interactions. The effectiveness of an inlet duct lining is reduced because acoustic energy is scattered into modes that are poorly absorbed by the liner. In this article, the effect of this acoustic scattering is examined by three-dimensional finite-element simulations of sound transmission in a turbofan inlet duct. Results include predictions of the sound power transmission loss with different splice widths, and at different supersonic fan speeds. These results demonstrate how acoustic scattering by liner splices can adversely affect fan tone noise levels at low supersonic fan speeds, but have little adverse affect on noise levels at high supersonic fan speeds. The potential noise benefit that could be achieved by manufacturing thinner splices is also examined.

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Published date: 9 May 2006

Identifiers

Local EPrints ID: 28000
URI: https://eprints.soton.ac.uk/id/eprint/28000
ISSN: 0022-460X
PURE UUID: 1b8a8e21-a3ca-4a81-9ac4-51f42502b2b0
ORCID for A. McAlpine: ORCID iD orcid.org/0000-0003-4189-2167

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Date deposited: 28 Apr 2006
Last modified: 15 Aug 2019 00:50

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Contributors

Author: A. McAlpine ORCID iD
Author: M.C.M. Wright

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