Boundary condition at the interface between air duct and porous material with rigid frame for the lined ducts with a grazed flow

Ygäal Renou , Yves Aurégan (1)

1 LAUM - Laboratoire d'Acoustique de l'Université du Mans

In flow ducts such as engine duct systems in aeroplanes, the reduction of noise is usually accomplished by means of materials composed of a perforated sheet backed by honeycomb cavities (also known as SDOF liners). In front of the complexity of modeling with accuracy the acoustic propagation superimposed with a turbulent grazing flow, especially in the sheared boundary layer, an uniform mean flow is widely assumed for the simplication of the computations. The associated boundary condition is well known as the Ingard-Myers condition assuming the continuity of normal particle displacement at the surface of the liner. The failure of this condition associated with uniform flow was recently demonstrated with an experimental approach. The results showed that a mixture between normal acoustic displacement and normal acoustic velocity must apply, depending on the relative importance of the stationnary flow and acoustic boundary layers thicknesses, respectively. The present study aims at providing an experimental identification of the adequate boundary condition at interface between the air duct and a porous material with rigid frame in presence of a grazed flow. The correct boundary condition is deduced by fitting the measured scattering matrix and the predicted scattering matrix computed by a spectral collocation method, the new boundary condition and an accurate mode-matching scheme.

Mots clés: Lined duct; Flow duct; Porous material; Bounday condition

Domaines: Acoustique [physics.class-ph]

Ygäal Renou, Yves Aurégan. Boundary condition at the interface between air duct and porous material with rigid frame for the lined ducts with a grazed flow. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00811329⟩