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Mode detection in turbofan inlets from acoustic pressure measurements in the radiated field

Mode detection in turbofan inlets from acoustic pressure measurements in the radiated field
Mode detection in turbofan inlets from acoustic pressure measurements in the radiated field
Knowledge of the modal content of the sound field radiated from a turbofan inlet is important for source characterisation and for helping to determine noise generation mechanisms in the engine. An inverse technique for determining the mode decomposition is proposed using pressure measurements from mode on the Turbulence Control Screen (TCS). The TCS offers a useful platform for locating microphones since they are often fitted to engines during ground testing to smooth the integrated flow. Array performance is tested on computer-generated data from modal radiation predictions using a model based on the Kirchhoff approximation for flanged ducts with no flow. An overdetermined system of linear equations that accounts for the radiation at the TCS due to all cut-on modes and nearly cut-on modes is constructed from this model and is inverted to determining mode amplitudes. The sensitivity of the reconstructed mode amplitudes to noise is determined by the condition number of the radiation matrix, containing modal directivity functions predicted at each sensor location. This paper discusses the number and configuration of microphones on the TCS needed for robust and accurate modal inversion. Finally, this paper discusses the use of constraining the solution by regularisation in order to improve inversion robustness to noise.
Castres, F.
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Joseph, P.F.
9c30491e-8464-4c9a-8723-2abc62bdf75d
Astley, R.J.
cb7fed9f-a96a-4b58-8939-6db1010f9893
Castres, F.
5740960c-c521-44c7-8fb0-aa7183403768
Joseph, P.F.
9c30491e-8464-4c9a-8723-2abc62bdf75d
Astley, R.J.
cb7fed9f-a96a-4b58-8939-6db1010f9893

Castres, F., Joseph, P.F. and Astley, R.J. (2004) Mode detection in turbofan inlets from acoustic pressure measurements in the radiated field. 10th AAIA/CEAS Aeroacoustics Conference, Manchester, UK. 09 - 11 May 2004. 16 pp .

Record type: Conference or Workshop Item (Paper)

Abstract

Knowledge of the modal content of the sound field radiated from a turbofan inlet is important for source characterisation and for helping to determine noise generation mechanisms in the engine. An inverse technique for determining the mode decomposition is proposed using pressure measurements from mode on the Turbulence Control Screen (TCS). The TCS offers a useful platform for locating microphones since they are often fitted to engines during ground testing to smooth the integrated flow. Array performance is tested on computer-generated data from modal radiation predictions using a model based on the Kirchhoff approximation for flanged ducts with no flow. An overdetermined system of linear equations that accounts for the radiation at the TCS due to all cut-on modes and nearly cut-on modes is constructed from this model and is inverted to determining mode amplitudes. The sensitivity of the reconstructed mode amplitudes to noise is determined by the condition number of the radiation matrix, containing modal directivity functions predicted at each sensor location. This paper discusses the number and configuration of microphones on the TCS needed for robust and accurate modal inversion. Finally, this paper discusses the use of constraining the solution by regularisation in order to improve inversion robustness to noise.

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More information

Published date: 2004
Additional Information: Volume: 2004-2953
Venue - Dates: 10th AAIA/CEAS Aeroacoustics Conference, Manchester, UK, 2004-05-09 - 2004-05-11

Identifiers

Local EPrints ID: 10397
URI: http://eprints.soton.ac.uk/id/eprint/10397
PURE UUID: 36dc46d5-8377-4e52-b9d3-7f4bd11eb3f8

Catalogue record

Date deposited: 29 Jun 2005
Last modified: 22 Jun 2021 16:31

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Contributors

Author: F. Castres
Author: P.F. Joseph
Author: R.J. Astley

University divisions

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