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On the attenuation of sound by three-dimensionally segmented acoustic liners in a rectangular ductAxial segmentation of acoustically absorbing liners in rectangular, circular or annual duct configurations is a very useful concept for obtaining higher noise attenuation with respect to the bandwidth of absorption as well as the maximum attenuation. As a consequence, advanced liner concepts are proposed which induce a modal energy transfer in both cross-sectional directions to further reduce the noise radiated from turbofan engines. However, these advanced liner concepts require three-dimensional geometries which are difficult to treat theoretically. A very simple three-dimensional problem is investigated analytically. The results show a strong dependence on the positioning of the liner for some incident source modes while the effect of three-dimensional segmentation appears to be negligible over the frequency range considered.
Document ID
19790019761
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Koch, W. (Institut fuer Theoretische Stroemungsmechanik DFVLR/AVA, Goettingen, Germany)
Date Acquired
September 3, 2013
Publication Date
June 1, 1979
Subject Category
Acoustics
Report/Patent Number
NASA-TM-80118
Accession Number
79N27932
Funding Number(s)
PROJECT: RTOP 505-03-13-18
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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