Abstract
In this paper, the effect of duct-lining anisotropy, with respect to flow resistivity, in particular, is considered. The duct lining is modeled by using a fully poroelastic theory derived from the Biot theory. The lining is considered to occupy only a part of the duct cross section, and is imagined to be infinite in length. When the appropriate solutions for the sound fields within the airway and the anisotropic porous material are substituted into the boundary conditions of the problem, a homogeneous system of equations results. The propagation characteristics of the duct modes can then be found by identifying the conditions under which the determinant of that system of equations is zero. Corresponding experiments have been conducted using samples of aviation-grade glass fiber partially lining a square-section, four-microphone standing wave tube. Excellent agreement between measured attenuations and predictions was found. It will be shown that the modal attenuation is primarily sensitive to the flow resistivity of the lining in the axial direction.
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