Three-Dimensional Study of Annular Chamber Mufflers using Green's Function Method

Keskar, Harshad Nitin (2016) Three-Dimensional Study of Annular Chamber Mufflers using Green's Function Method. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

A major area of interest in a muffler design is in its acoustic and ow performance. Other parameters in design are weight, availability of space and reliability of operation. Transmission Loss (TL) and Insertion Loss (IL) of a muffler are good indicators of acoustical performance. These values are computed by using methods such as one-dimensional transfer matrix, two-dimensional mode matching method, Green's function method, Finite-Element Method (FEM) and Boundary Element Method (BEM). Pressure drops across muffler influence its functioning. It is known that acoustic and ow performance parameters are contradicting. An efficient muffler design should have a minimum pressure drop and as high transmission loss as possible. Extended Inlet and Extended Outlet (EIEO)muffler has a wider frequency band acoustical performance as compared to a Simple Expansion Chamber (SEC). A methodology is developed for EIEO muffler to optimize both acoustic and ow parameters using one-dimensional study. This study works well for low to medium operating frequencies. As the chamber parameters change, one-dimensional analysis is not alone sufficient. The high-frequency waves, due to their short wave-length, tend to travel in all the three directions. The plane-wave assumption does not hold for short chamber mufflers. To get more accurate results, a three-dimensional methodology is more suitable. An EIEO muffler can be considered as a combination of circular and annular cavities. Literature to estimate the transmission loss of circular cavity, analytically using Green's function has already been developed. Thus, an analytical approach for the transmission loss characteristics of an annular cavity with arbitrary locations of inlet and outlet ports has been established in this thesis. The analytically obtained results for various configurations are validated numerically using FEM software. The analytical results were found to be in good agreement with those obtained using finite element method.

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