The absorption of axial acoustic waves by a perforated liner with bias flow

Abstract

The effectiveness of a cylindrical perforated liner with mean bias flow in its absorption of planar acoustic waves in a duct is investigated. The liner converts acoustic energy into flow energy through the excitation of vorticity fluctuations at the rims of the liner apertures. A one-dimensional model that embodies this absorption mechanism is developed. It utilizes a homogeneous liner compliance adapted from the Rayleigh conductivity of a single aperture with mean flow. The model is evaluated by comparing with experimental results, with excellent agreement. We show that such a system can absorb a large fraction of incoming energy, and can prevent all of the energy produced by an upstream source in certain frequency ranges from reflecting back. Moreover, the bandwidth of this strong absorption can be increased by appropriate placement of the liner system in the duct. An analysis of the acoustic energy flux is performed, revealing that local differences in fluctuating stagnation enthalpy, distributed over a finite length of duct, are responsible for absorption, and that both liners in a double-liner system are absorbant. A reduction of the model equations in the limit of long wavelength compared to liner length reveals an important parameter grouping, enabling the optimal design of liner systems.

Acoustic modeling of perforated plates with bias flow for Large-Eddy Simulations

“…His results were notably confirmed by the subsequent experiments of Hughes and Dowling (1990) and Eldredge and Dowling (2003). Three models are presented in the next paragraphs.…”

“…First, perforated plates are communications between the combustion chamber and the casing, which is likely to influence the acoustic modes of the complete chamber. Moreover, it has been demonstrated, both analytically (Howe, 1979(Howe, , 1998, experimentally (Hughes and Dowling, 1990;Eldredge and Dowling, 2003;Tran et al, 2007) and numerically (Eldredge et al, 2007;Dassé et al, 2008) that perforated plates have a damping effect on incident acoustic waves and thus potentially on combustion instabilities. The sound attenuation mechanism consists in the conversion of acoustic energy into vortical energy (Bechert, 1979;Howe, 1979;Tam et al, 2001): incident waves interact with the shear layers formed at the apertures rims; subjected to pressure fluctuations, the shear layers destabilize to form vortex rings.…”

“…For certain frequencies, depending on the geometrical and operating characteristics, an incident acoustic wave can be almost completely damped by a system composed by a perforated liner and a back wall (Hughes and Dowling, 1990;Bellucci et al, 2004), which is exactly what is encountered in combustion chambers, the back wall being the wall bounding the casing. Moreover, perforated liners are also effective to absorb sound of grazing acoustic waves (Eldredge and Dowling, 2003). Grazing acoustic waves are characteristic of both longitudinal and azimuthal modes, which are the most energetic modes in combustion chambers.…”

High-speed camera-based measurement system for aeroacoustic investigations

“…1 are used (Eldredge and Dowling, 2003). By applying a bias flow through the perforation of such liners it is possible to increase the efficiency and bandwidth of the damping effect (Bechert, 1980).…”

Acoustic Models for Cooled Helmholtz Resonators

“…1 (left)), while linear models suffice in the presence of a mean neck flow (see Fig. 1 (middle)) [2][3][4][5].…”