Flow-Acoustic Analysis of the Perforated-Baffle Three-Chamber Hybrid Muffler Configurations 2015-26-0131

In this work, the noise attenuation characteristics of a three-chamber U-bend hybrid muffler have been investigated. Acoustic performance is quantified by the Transmission Loss (TL) parameter. One-dimensional Transfer Matrix based Muffler Program (TMMP) and three-dimensional Finite Element Method (FEM) have been used for the prediction of the TL of the muffler. Presence of perforated baffles necessitates use of the Integrated Transfer Matrix (ITM) approach for the one-dimensional analysis because the sound fields in the adjacent chambers would be multiply coupled with each other, and for the 3D FEM analysis LMS Virtual Lab software has been used. The mean flow distribution in each of these configurations has been evaluated by means of a lumped flow resistance network. The resulting values of the grazing flow and bias flow have been used to calculate the perforates' acoustic impedance. TL calculated with the help of the 1D analysis shows good agreement with the simulated results from the 3D FEA. Apart from the three-chamber U-bend hybrid muffler, three additional configurations have been analyzed, and the effects of the absorptive material, porosity of the baffle plates, porosity of the perforated pipes, and the length of perforation of the perforated pipes have been studied. Based on the above studies, design guidelines have been developed for these types of muffler configurations in order to improve their performance.