title: Acoustic of a perforated liner with grazing flow: Floquet-Bloch periodical approach versus impedance continuous approach.
abstract: The effect of a shear flow on an acoustic liner consisting of a perforated plate backed by cavities is studied. Two different approaches are investigated: First, the duct and the liner are considered as a periodic system while in the second approach the liner is considered as homogeneous and described by an impedance. Those two approaches coincide perfectly without flow for a small hole spacing compared to the acoustic wavelength. This work demonstrates that those two approaches are not wholly consistent when a shear flow is present and reveals some problems in the use of the local impedance with flow. The no-flow impedance cannot be used to describe the liner when a shear flow is present. An equivalent impedance with flow can be defined but it depends on the direction of the incident waves and loses its local characteristic.
authors.affiliation: Laboratoire d'Acoustique de l'Université du Maine, UMR CNRS 6613, Avenue O Messiaen, F-72085 LE MANS Cedex 9, France.
authors.forename: Xiwen
authors.initials: X
authors.lastname: Dai
authors.affiliation: Laboratoire d'Acoustique de l'Université du Maine, UMR CNRS 6613, Avenue O Messiaen, F-72085 LE MANS Cedex 9, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Aurégan