A measurement method for determining the source data of acoustic two-port sources

“…Several methods for the determination of the transfer impedance of these elements can be found in literature, [9]. In this work, the 2-port data of the samples have been experimentally determined in order to carry out the associated transfer impedance, [26]. The sound field propagating in the test-rig below the first cut-on frequency consists of plane waves.…”

Section: Transfer Impedance Measurementmentioning

confidence: 99%

Acoustic performance of micro-grooved elements

Auriemma

2017

Applied Acoustics

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The acoustic performance of a new type of fibre-less sound absorber, the Micro-Grooved Element (MGE), is studied in this paper. The transfer impedance and the absorption coefficient of micro-grooved and Micro-Perforated Elements (MPEs) are measured, modelled and compared.A MGE is a double layer element that involves inlet/outlet slots and facing micro-channels engraved onto the mating surface of the layers. The main advantage of these elements is that, by means of a simple technological process, thin micro-channels with depth of less then 100µm can be easily engraved. This allows the MGEs exhibiting higher absorption coefficients compared to traditional MPEs with 300−700µm diameter of perforations. Moreover, due to the presence of surfaces surrounding the micro-channels, the MGEs show reduced resistance when exposed to high level of sound excitation. In this perspective, the performance of a MGE is more stable than the one of a MPE provided with the same porosity.A number of different MGEs with varied internal geometries has been tested at different excitation levels. The acoustics of the micro-channels is treated in details, the impedance end corrections are determined and the non-linear effects are accounted for. The linear behaviour of MGEs is described by adapting the models for slit-shaped perforated elements (SSEs). The quasi-and non-linear behaviours are expressed as a function of the Shear number and Strouhal number by curve fitting the experimental results.

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“…L'utilisation de ces codes requiert l'introduction des informations qui permettent de représenter le comportement des divers composants : pour des éléments complexes, telles les pompes ou les turbines en fonctionnement, cette caractérisation n'est à ce jour accessible qu'expérimentalement. Il faut noter que des techniques équivalentes sont utilisées pour la caractérisa-tion aéro-acoustique d'éléments de circuits aérauliques (ventilateurs, tubulures d'échappement ou d'admission de moteurs,... [7,8] [9]. Les quatre termes de l'une ou l'autre de ces matrices sont des fonctions complexes de la fréquence f et constituent les inconnues lors de la détermination expérimentale de ces caractéristiques de transfert.…”

Section: • Introductionunclassified