On the efficiency of parallel baffle-type silencers in rectangular ducts: prediction and measurement

Overview & Synopsis

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.