A Basic Study on Acoustic Response of Non-symmetric Perforated Duct Mufflers

Perforated sections are common constituent elements of the commercial mufflers used to control the acoustic performance of the silencer, guide the flow and hold the absorbing material when incorporated. The effect of the geometrical parameters such as hole diameter and porosity on the acoustic response of non-concentric perforated duct muffler has been investigated experimentally using a modified impulse method. The experimental study showed that the acoustic behavior is basically determined by one single geometrical parameter: the modified porosity defined as the ratio between the perforated area and the tube cross section area. Furthermore, a one-dimensional time-domain simulation of the investigated geometries was performed. In this connection, the perforated tube muffler was modeled by an equivalent acoustic system, composed of simple zero- and one-dimensional elements, which incorporate the main attenuation mechanisms present in the muffler. The comparison between the measured and calculated acoustic attenuation has been conducted for a broad range of modified porosities. It showed that the proposed computational methodology can yield results in very good agreement with the experimental data for the high modified porosities. However, low modified porosities of non-concentric perforated tube muffler lead to systematic error in prediction of the transmission loss with increasing the frequency. This indicates a complex frequency dependent influence of the perforation impedance for low perforated fractions.