Transmission Loss analysis of a simple expansion chamber muffler with extended inlet and outlet combined with inhomogeneous micro-perforated panel (iMPP)

Abstract

This paper studies the acoustic performance of a simple expansion chamber muffler combined with an inhomogeneous microperforated panel (iMPP). Three different shaped mufflers, i.e., circular, rectangular, and elliptical, with extended inlet and outlet pipes, have been studied. The thermo-acoustic module of COMSOL Multiphysics 5.5a software is used for finite element method (FEM) simulation. Then the 3D printing (stereolithography) technology is used to manufacture the samples. The transmission loss (TL) of the muffler given by the FEM simulation model is verified and measured by the Two-load method experiment, and the muffler with and without iMPP is tested. Different configurations have been tested to detect the effect of resonator absorbers based on iMPP in the expansion chambers. To observe the effectiveness of using iMPP, it is compared with other homogeneous MPPs. The results show that the TL of the low to medium frequency region increases by 25∼30 dB after adding iMPPs into the expansion chamber. Finally, the air-cavity depth behind the iMPP and the length of the expansion chamber is varied to study its effect on TL performance. The results show that the larger the cavity depth, the lower the TL peak. At the same time, with the decrease of the expansion chamber length, the TL peak gradually decreases and narrows. By carefully controlling and selecting the iMPP and expansion chamber parameters, we can obtain the required TL. Therefore, when the reactive effect of the muffler becomes invalid, iMPP can be used as an alternative further to improve the TL from low frequency to medium frequency.