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After-body liner performance predictions on bypass exhaust fan noise with a simple 3/4 cowl geometry and coaxial mean flow

After-body liner performance predictions on bypass exhaust fan noise with a simple 3/4 cowl geometry and coaxial mean flow
After-body liner performance predictions on bypass exhaust fan noise with a simple 3/4 cowl geometry and coaxial mean flow
Aft fan noise is becoming a more dominant source as engine bypass ratio is increased and improved methods are required for its control. Bypass liners are especially effective in attenuating aft fan noise, but, in recent papers we introduced the idea of using acoustic linings on external parts of the aero-engine nacelle, such as the afterbody and plug nozzle. We showed that when the afterbody is acoustically lined, it can reduces the far field broadband sound power by up to 3 dB in the absence of flow, an experimental result which was confirmed with calculations using a commercially available CAA code. In this paper, we extend the previous computations to include the effects of a two-stream coaxial flow using the same CAA code but with a new 1D membrane element to represent the shear layers. The results, supported by two analytical models, confirm our expectations that the AL could also provide significant reductions in aft fan with flow. As anticipated the main flow effect is to refract the no-flow insertion loss to larger angles outside the cone of silence, with little or no benefits inside the cone of silence. However, it should be emphasised that although the results obtained so far are with a representative mean flow, the geometry is still idealized and these and other computations have to be validated with data from large-scale tests based on a fully realistic geometry and flow.
De Mercato, L.
0be28cbb-dae1-49b8-847b-62683ef86231
Tester, B.
1bd4a793-131b-4173-93cc-3eca70b2d116
Demir, A.
e93ef183-723f-4dbc-a1b7-a32d355e266e
De Mercato, L.
0be28cbb-dae1-49b8-847b-62683ef86231
Tester, B.
1bd4a793-131b-4173-93cc-3eca70b2d116
Demir, A.
e93ef183-723f-4dbc-a1b7-a32d355e266e

De Mercato, L., Tester, B. and Demir, A. (2008) After-body liner performance predictions on bypass exhaust fan noise with a simple 3/4 cowl geometry and coaxial mean flow. Proceedings of the 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference). 05 - 07 May 2008.

Record type: Conference or Workshop Item (Paper)

Abstract

Aft fan noise is becoming a more dominant source as engine bypass ratio is increased and improved methods are required for its control. Bypass liners are especially effective in attenuating aft fan noise, but, in recent papers we introduced the idea of using acoustic linings on external parts of the aero-engine nacelle, such as the afterbody and plug nozzle. We showed that when the afterbody is acoustically lined, it can reduces the far field broadband sound power by up to 3 dB in the absence of flow, an experimental result which was confirmed with calculations using a commercially available CAA code. In this paper, we extend the previous computations to include the effects of a two-stream coaxial flow using the same CAA code but with a new 1D membrane element to represent the shear layers. The results, supported by two analytical models, confirm our expectations that the AL could also provide significant reductions in aft fan with flow. As anticipated the main flow effect is to refract the no-flow insertion loss to larger angles outside the cone of silence, with little or no benefits inside the cone of silence. However, it should be emphasised that although the results obtained so far are with a representative mean flow, the geometry is still idealized and these and other computations have to be validated with data from large-scale tests based on a fully realistic geometry and flow.

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More information

Published date: May 2008
Additional Information: Paper Number: AIAA-2008-2881
Venue - Dates: Proceedings of the 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), 2008-05-05 - 2008-05-07

Identifiers

Local EPrints ID: 57784
URI: https://eprints.soton.ac.uk/id/eprint/57784
PURE UUID: 7f8fcffb-5f0e-407e-b450-fd86b2beafec

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Date deposited: 20 Aug 2008
Last modified: 13 Mar 2019 20:33

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