Duct modes damping through an adjustable electroacoustic liner under grazing incidence

R Boulandet,H Lissek,S Karkar,M Collet,G Matten,M Ouisse,M Versaevel

doi:10.1016/j.jsv.2018.04.009

Abstract

This paper deals with active sound attenuation in lined ducts with flow and its application to duct modes damping in aircraft engine nacelles. It presents an active lining concept based on an arrangement of electroacoustic absorbers flush mounted in the duct wall. Such feedback-controlled loudspeaker membranes are used to achieve locally reacting impedances with adjustable resistance and reactance. A broadband impedance model is formulated from the loudspeaker parameters and a design procedure is proposed to achieve specified acoustic resistances and reactances. The performance is studied for multimodal excitation by simulation using the finite element method and the results are compared to measurements made in a flow duct facility. This electroacoustic liner has an attenuation potential comparable to that of a conventional passive liner, but also offers greater flexibility to achieve the target acoustic impedance in the low frequencies. In addition, it is adaptive in real time to track variable engine speeds. It is shown with the liner prototype that the duct modes can be attenuated over a bandwidth of two octaves around the resonance frequency of the loudspeakers.

Highlights

Challenging noise reduction targets, such as those specified in the European FlightPath 2050 goals, require aircraft manufacturers to develop innovative lining technologies to limit noise emission in the vicinity of airports
We provide numerical and experimental results that show the performance of the active electroacoustic liner described in Section 2, both in the absence and presence of flow
The results presented below correspond to a set of specific values and are intended to show the capability of the electroacoustic liner to achieve broadband performance

Summary

Introduction

Challenging noise reduction targets, such as those specified in the European FlightPath 2050 goals, require aircraft manufacturers to develop innovative lining technologies to limit noise emission in the vicinity of airports. The lining specifications are usually given in terms of desired acoustic resistance and reactance, which depend on several factors related to the excitation frequency, the duct geometry and dimension, the characteristics of propagating modes, and the presence or absence of airflow through the duct [1, 2, 3]. Conventional acoustic liners such as Single Degree of Freedom (SDOF) liners consist of a thin layer of perforated plate or wire-mesh face sheet backed with a honeycomb cavity, with internal partitions closed by an impervious plate, which provide an essentially locally reacting surface.

Methods

Results

Discussion

Conclusion