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"Buzz-saw" noise: prediction of the rotor-alone pressure field

"Buzz-saw" noise: prediction of the rotor-alone pressure field
"Buzz-saw" noise: prediction of the rotor-alone pressure field
Public expectations of lower environmental noise levels, and increasingly stringent legislative limits on aircraft noise, result in noise being a critical technical issue in the development of jet engines. Noise at take-off, when the engines are at high-power operating conditions, is a key reference level for engine noise certification. ‘‘Buzz-saw’’ noise is the dominant fan tone noise from modern high-bypass-ratio turbofan aircraft engines during take-off. Rotor-alone tones are the key component of buzz-saw noise. The rotor-alone pressure field is cut-off at subsonic fan tip speeds; buzz-saw noise is associated with supersonic fan tip speeds, or equivalently, high power engine operating conditions. A recent series of papers has described new work concerning the prediction of buzz-saw noise. The prediction method is based on modelling the nonlinear propagation of onedimensional sawtooth waveforms. A sawtooth waveform is a simplified representation of the rotor-alone pressure field. Previous validation of the prediction method focussed entirely on reproducing the spectral characteristics of buzz-saw noise; this was dictated at that time by the availability of spectral data only for comparison between measurement and prediction. In this paper, full validation of the method by comparing measurement and prediction of the rotor-alone pressure field is published for the first time. It is shown that results from the modelling based on a one-dimensional sawtooth waveform capture the essential features of the rotor-alone pressure field as it propagates upstream inside a hardwalled inlet duct. This verifies that predictions of the buzz-saw noise spectrum, which are in good agreement with the measured data, are based on a model which reproduces the key physics of the noise generation process. Validation results for the rotor-alone pressure field in an acoustically lined inlet duct are also shown. Comparisons of the measured and predicted rotor-alone pressure field are more difficult to interpret because the acoustic lining significantly modifies the sawtooth waveform, but there remains good agreement with the measured spectral data. The buzz-saw noise prediction code used to generate the simulations in this paper has been used by the Rolls–Royce Noise Department since 2004.
0022-460X
4901-4918
McAlpine, A.
aaf9e771-153d-4100-9e84-de4b14466ed7
Schwaller, P.J.G.
14b13d54-54dc-4fb2-ba56-35026930a68a
Fisher, M.J.
9662c037-03c2-4a45-9b58-9b83fe5b323d
Tester, B.J.
1bd4a793-131b-4173-93cc-3eca70b2d116
McAlpine, A.
aaf9e771-153d-4100-9e84-de4b14466ed7
Schwaller, P.J.G.
14b13d54-54dc-4fb2-ba56-35026930a68a
Fisher, M.J.
9662c037-03c2-4a45-9b58-9b83fe5b323d
Tester, B.J.
1bd4a793-131b-4173-93cc-3eca70b2d116

McAlpine, A., Schwaller, P.J.G., Fisher, M.J. and Tester, B.J. (2012) "Buzz-saw" noise: prediction of the rotor-alone pressure field. Journal of Sound and Vibration, 331 (22), 4901-4918. (doi:10.1016/j.jsv.2012.06.009).

Record type: Article

Abstract

Public expectations of lower environmental noise levels, and increasingly stringent legislative limits on aircraft noise, result in noise being a critical technical issue in the development of jet engines. Noise at take-off, when the engines are at high-power operating conditions, is a key reference level for engine noise certification. ‘‘Buzz-saw’’ noise is the dominant fan tone noise from modern high-bypass-ratio turbofan aircraft engines during take-off. Rotor-alone tones are the key component of buzz-saw noise. The rotor-alone pressure field is cut-off at subsonic fan tip speeds; buzz-saw noise is associated with supersonic fan tip speeds, or equivalently, high power engine operating conditions. A recent series of papers has described new work concerning the prediction of buzz-saw noise. The prediction method is based on modelling the nonlinear propagation of onedimensional sawtooth waveforms. A sawtooth waveform is a simplified representation of the rotor-alone pressure field. Previous validation of the prediction method focussed entirely on reproducing the spectral characteristics of buzz-saw noise; this was dictated at that time by the availability of spectral data only for comparison between measurement and prediction. In this paper, full validation of the method by comparing measurement and prediction of the rotor-alone pressure field is published for the first time. It is shown that results from the modelling based on a one-dimensional sawtooth waveform capture the essential features of the rotor-alone pressure field as it propagates upstream inside a hardwalled inlet duct. This verifies that predictions of the buzz-saw noise spectrum, which are in good agreement with the measured data, are based on a model which reproduces the key physics of the noise generation process. Validation results for the rotor-alone pressure field in an acoustically lined inlet duct are also shown. Comparisons of the measured and predicted rotor-alone pressure field are more difficult to interpret because the acoustic lining significantly modifies the sawtooth waveform, but there remains good agreement with the measured spectral data. The buzz-saw noise prediction code used to generate the simulations in this paper has been used by the Rolls–Royce Noise Department since 2004.

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e-pub ahead of print date: 10 July 2012
Published date: 22 October 2012
Organisations: Acoustics Group

Identifiers

Local EPrints ID: 341389
URI: http://eprints.soton.ac.uk/id/eprint/341389
ISSN: 0022-460X
PURE UUID: 1fb6f064-d396-40c1-933e-26a670e1d5de
ORCID for A. McAlpine: ORCID iD orcid.org/0000-0003-4189-2167

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Date deposited: 23 Jul 2012 14:21
Last modified: 15 Mar 2024 03:00

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Contributors

Author: A. McAlpine ORCID iD
Author: P.J.G. Schwaller
Author: M.J. Fisher
Author: B.J. Tester

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