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COMPORTEMENT DES MATERIAUX ABSORBANTS DANS LES CHAMPS ACOUSTIQUES INTENSES ; MODELISATION DE TRAITEMENTS ACOUSTIQUES REACTIFS A REACTION NON LOCALE DANS LES CONDUITS

Abstract : This work is a contribution to an improved noise reduction provided acoustic treatments, such as aircraft turbofan engines liners or automotive mufflers The first part deals with the behavior of acoustic porous materials under high incident sound pressure levels, when the skeleton is motionless. Two experimental set-ups are presented. The first one determines the flow resistivity of a porous sample as a function of the Reynolds number of the flow in the sample (on linear Darcy law). The measurement exhibit two different non linear behavior; one of these is the classical Forchheimer law (high Reynolds: numbers), the other one being a quadratic function of the Reynolds numbers without linear term as far as the Reynolds number is under a critical value which is determined from the measurement. The second set- up gives the acoustic reflection and transmission coefficient of a porous sample inserted in a tube, as a function of frequency (80-800 Hz ) and incident sound pressure level (110-150 dB ref. 2.10-5 Pa). A semi-empirical model is presented. Accordance between predicted and measured reflection and transmission coefficient is satisfactory. The second part deals with reactive and non-locally reacting liners. Helmholtz resonators are known to be be efficient in order to muffle inlet and outlet ducts of an aircraft turbofan engines. Let open a hole in the sidewall of the resonators; thus the acoustic fields in the resonators are coupled. This type of acoustic treatment is no more locally reacting (wall impedance) and must be considered as a wave guide coupled to the inlet or outlet duct. Firsts as analytical model is presented for a large duct lined with such coupled Helmholtz resonators. Then, an analytical model is given for the acoustic propagation in at lattice made of two parallel waveguides periodically coupled by means of lateral perforations. The solutions of the dispersion equation (infinite length lattice) and the insertion loss (finite length) are given analytically, using formalism of periodic media (discrete model). These results are illustrated by calculating the sound attenuation of a classical automotive perforated tube muffler with added discontinuities, exhibiting the resonant maxima provided by the interferences of the two propagating modes of the lattice.
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https://tel.archives-ouvertes.fr/tel-00494951
Contributor : Marc Pachebat <>
Submitted on : Thursday, June 24, 2010 - 12:34:38 PM
Last modification on : Tuesday, November 3, 2020 - 1:04:02 PM
Long-term archiving on: : Thursday, December 1, 2016 - 4:39:16 PM

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  • HAL Id : tel-00494951, version 1

Citation

Marc Pachebat, Jean-François Allard. COMPORTEMENT DES MATERIAUX ABSORBANTS DANS LES CHAMPS ACOUSTIQUES INTENSES ; MODELISATION DE TRAITEMENTS ACOUSTIQUES REACTIFS A REACTION NON LOCALE DANS LES CONDUITS. Acoustique [physics.class-ph]. Université du Maine, 1997. Français. ⟨tel-00494951⟩

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