A tunable acoustic liner

Abstract

An experimental program is performed that assesses a concept that controls perforate impedance and thus controls the performance of resonant liners. Using two perforates, one on top of the other, a tunable liner is formed which is accomplished by varying the overall perforate's porosity. Normal incident impedance measurements are made of this type of perforate to assess its potential. In addition,, the variable perforate is used in a 2DOF resonant liner as the septum layer. Results of this preliminary proof-of-concept study indicate that a large degree of impedance change can be realized with a small amount of relative movement of the two perforate layers. Control of the a 2DOF liner's peak absorption frequency as well as its overall performance is also demonstrated in a flow-duct environment. Nomenclature

A Requirements-Driven Optimization Method for Acoustic Treatment Design

“…The result is a 1 ft lossless narrowband static noise surrogate model of the fan, L Lf; θ; N, that can be projected to arbitrary flight conditions using Eqs. (4) and (5). The flight conditions at each certification noise monitor (shown in Table 3) are typical of a narrow-body 737-or A320-class transport.…”

“…A dynamically changing source may be more effectively suppressed with active and adaptive liners. Gaeta and Ahuja [5], for example, experimented with tunable acoustic liners in 1998. Now, shape-memory materials and other techniques are enabling morphing, more tunable liner geometries that can adjust to a changing noise source by tailoring its suppression spectrum.…”

Modeling, design, and optimization of a dielectric elastomer acoustic liner

“…The facesheet hole area was changed in Nagaya et al 4 where the peak resonant frequency was tuned by 200 Hz. The porous septum of a 2DOF liner was misaligned to reduce the percent open area in Gaeta et al 5 and a reduction in the resonant frequency of approximately 100 Hz, or 16% was observed. However, such designs often require large moving parts that can be heavy, complex, and require significant amounts of energy.…”

A Requirements-Driven Optimization Method for Acoustic Liners using Analytic Derivatives

“…A dynamically-changing source may be more effectively suppressed with active and adaptive liners having variable impedance. Gaeta and Ahuja [6], for example, experimented with tunable acoustic liners in 1998. Now, shape-memory materials and other techniques are enabling morphing, more-tunable liner geometries that can adjust to a changing noise source by tailoring its suppression spectrum.…”