Medições de impedância acústica de liners com escoamento tangencial e elevado NPS: uma visão geral do rig de teste do LVA/UFSC

Acoustic Liner Impedance Measurements with Grazing Flow and High SPL: an Overview of the LVA/UFSC Test Rig

Quintino, N. T. Laboratório de Vibrações e Acústica, Universidade Federal de Santa Catarina, Florianópolis, SC, Brasil, nicolas.quintino@lva.ufsc.br

Bonomo, L. A. Laboratório de Vibrações e Acústica, Universidade Federal de Santa Catarina, Florianópolis, SC, Brasil, lucas.bonomo@lva.ufsc.br

Spillere, A. M. N. Laboratório de Vibrações e Acústica, Universidade Federal de Santa Catarina, Florianópolis, SC, Brasil

Cordioli, J. A. Laboratório de Vibrações e Acústica, Universidade Federal de Santa Catarina, Florianópolis, SC, Brasil, julio.cordioli@ufsc.br

Resumo

Liners acústicos utilizados em aeronaves turbofan para atenuar o ruído do fan são representados pela sua impedância acústica. Sabe-se que essa impedância acústica varia com as condições operacionais, como o escoamento tangencial e o nível de pressão sonora. Existem vários métodos experimentais para medir a impedância acústica de liners sob essas condições, o que requer rigs de teste especializados. Este artigo apresenta uma visão geral do rig de teste do LVA/UFSC, que permite medições de impedância acústica com escoamento tangencial com número de Mach médio até 0,6 e nível de pressão sonora até 150 dB. Técnicas de medição in-situ já bem conhecidas são comparadas com os chamados métodos de edução, onde o campo acústico medido ao longo do duto é utilizado para extrair a impedância acústica do liner, baseada em modelos de propagação. As principais vantagens de cada método serão destacadas através da comparação de resultados.

Palavras-chaves:

liners

impedância acústica

bancada de medições.

Abstract

Acoustic liners used on turbofan aeroengines to fan noise suppres are represented by its acoustic impedance. This acoustic impedance is known to vary with operational conditions, such as grazing flow speed and sound pressure level. Several experimental methods for measuring the acoustic impedance of liners under such conditions, which requires specialized test rigs. This paper presents an overview of the LVA/UFSC Test Rig, which allows measurements of acoustic impedance with grazing flow with average Mach number up to 0.6 and sound pressure level up to 150 dB. The well known in-situ impedance measurement techniques is compared to the so-called eduction methods, where the acoustic field measured along the duct is used to extract the acoustic liner impedance, based on propagation models. The main advantages of each method will be highlighted along the comparison of the results.

Keywords:

liners

acoustic impedance

test rig.

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