On the Efficiency of Parallel Baffle-Type Silencers in Rectangular Ducts: Prediction and Measurement

Abstract

To estimate the efficiency of parallel baffle-type silencers in rectangular ducts, a two-dimensional multi-layer model is presented for predicting their transmission loss. The approach takes into account an arbitrary number of bulk reacting baffles of finite length bounded at both ends by a metallic fairing. Each layer is described by a mean pressure, which allows computing a piecewise constant modal basis for the mean pressure over the cross section. The continuity between the incoming and outgoing waves is performed by axial mode matching at the inlet and outlet cross-sections of the baffle silencer. It is shown that the model is easy to implement and suitable for optimization purposes based on design parameters such as the height of each baffle, their relative positions in the duct, and material properties. Relatively complex configurations can be simulated with relatively modest computational effort. An experimental campaign was carried out on a reduced scale test bench for standard configurations. The numerical results are in good agreement with the measurements. Noise reduction performances are analyzed in terms of reflected and dissipated sound powers. Finally, more complex geometric configurations are simulated in order to examine the influence of the relative transverse and axial positions of each baffle as well as the effect of a resistive screen between the baffles and the airways.

A homogenization method used to predict the performance of silencers containing parallel splitters

“…7 For the latter, the axial wavenumber b corresponding to the fundamental mode is considered. The locations of these maximums are in good agreement though discrepancies may occur in regions where Jm k dp is nearly constant with respect to the resistivity.…”

“…[1][2][3][4][5][6][7] Eigenfunctions can be solved either analytically, 5 using a root finding algorithm, 3,6 or by discretization techniques using trigonometric function decomposition, 1,2 the finite element method, 4 or layered discretizations. 7 It is also possible to perform three-dimensional finite element analysis. 8,9 A comparison between some of these methods can be found in the recent review of Kirby 8 on modeling automotive dissipative silencers.…”

Propagation of Acoustic Waves in Two Waveguides Coupled by Perforations. II. Analysis of Periodic Lattices of Finite Length

“…The characteristic impedances of the two guides, z i /h i (see Equations. (19,20), are found to be either infinite ou zero. It is interesting to interpret these results.…”

Poroelastic lamellar metamaterial for sound attenuation in a rectangular duct

“…The mitigation of these noise disturbances is usually accomplished using passive treatments by either using acoustic liners which consists in treating the wall of the duct adequately or by inserting dissipative splitter silencers in the duct. In the latter case, silencers are made with fibrous materials such as rock wool or glass fibre and are thus less effective at low frequency and for best sound attenuation, it is normally required that the thickness of the treatment should be of the same order as the acoustic wavelength [1][2][3]. Traditional acoustic liners, made of a resistive perforated plate coupled to a quarter-wavelength resonator, somewhat suffers from the same limitation as low frequency performances are typically limited by the cavity depth.…”