title: Experimental observation of a hydrodynamic mode in a flow duct with a porous material.
abstract: This paper experimentally investigates the acoustic behavior of a homogeneous porous material with a rigid frame (metallic foam) under grazing flow. The transmission coefficient shows an unusual oscillation over a particular range of frequencies which reports the presence of an unstable hydrodynamic wave that can exchange energy with the acoustic waves. This coupling of acoustic and hydrodynamic waves becomes larger when the Mach number increases. A rise of the static pressure drop in the lined region is induced by an acoustic excitation when the hydrodynamic wave is present.
authors.affiliation: Laboratoire d'Acoustique de l'Université du Maine, Unité Mixte de Recherche 6613 Centre National de la Recherche Scientifique, Avenue O Messiaen, F-72085 Le Mans Cedex 9, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Aurégan
authors.affiliation: Department of Mathematics and Computer Science, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
authors.forename: Deepesh Kumar
authors.initials: DK
authors.lastname: Singh