Passive Layer Optimization for Active Absorbers in Flow Duct Applications

Abstract

A new kind of acoustic liners developed for broadband noise reduction in flow duct applications is considered in this paper. Noise control is achieved by hybrid cells combining absorbent properties of a porous layer and active control. The main purpose is to realize an optimal impedance theoretically determined for a specific flow duct, in order to reach maximal sound attenuations over a wide frequency bandwidth. Passive and active optimization proceedings are carried out separately. This article deals with the complete design process of the hybrid liner passive part. Some experimental comparisons between active and passive functionning of the cells, obtained in our laboratory facility, are presented.

A multi-channel feedback algorithm for the development of active liners to reduce noise in flow duct applications

“…The effect of flow velocity is especially felt at low frequencies. ANC is worthwhile up to the cut-off frequency of 1.8 kHz, which is in good agreement with the theoretical predictions developed by Sellen et al [11]. The passive treatment takes over at higher frequencies.…”

“…Later, our team applied adaptive algorithms to achieve active control of the real part of the impedance (Furstoss et al [6]). Subsequent studies focused on the development of this technology for flow duct and nacelle applications [9][10][11][12]. Thanks to the double functioning mode of the resulting hybrid cells, the frequency bandwidth over which the efficiency is high is enlarged with respect to conventional passive treatments and purely active technologies.…”

Multi-cell Digital Feedback Control for Noise Reduction Through Hybrid Absorbers

“…The porous layer choice is also an important step in the realization of an appropriate adaptive liner for a given configuration. Other measurements especially with passive absorbers are available in the related paper 7 . Comparisons with classical passive treatments such as honeycomb and active configurations are presented to see the most frequency range efficiency.…”

“…Using a highly resistive material as the porous layer and a piezo-electric transducer as the secondary source, a thin hybrid liner called the hybrid cell is achieved [2][3][4] (see figure 1). The resistive layer optimization will not be considered here but is developed in another related paper 7 . Instead, this paper deals with the control aspect of this hybrid cell.…”

Experimental implementation of acoustic impedance control by a 2D network of distributed smart cells

“…The classical approaches [5,8] used by many authors studying the implementation of active acoustic impedance, such as Galland et al [9,10] for example, are based on the knowledge of the so-called optimal complex impedance, which they tend to implement experimentally using hybrid parietal ANC systems. Their purpose is to locally control a boundary interface to follow the pre-established frequency-dependent complex impedance.…”