Abstract
A substantial quantity of research on muffler design has been restricted
to a low frequency range using the plane wave theory. Based on this
theory, which is a one-dimensional wave, no higher order wave has been
considered. This has resulted in underestimating acoustical performances
at higher frequencies when doing muffler analysis via the plane wave
model. To overcome the above drawbacks, researchers have assessed a
three-dimensional wave propagating for a simple expansion chamber muffler.
Therefore, the acoustic effect of a higher order wave (a high frequency
wave) is considered here. Unfortunately, there has been scant research on
expansion chamber mufflers equipped with baffle plates that enhance noise
elimination using a higher-order-mode analysis. Also, space-constrained
conditions of industrial muffler designs have never been properly
addressed. So, in order to improve the acoustical performance of an
expansion chamber muffler within a constrained space, the optimization of
an expansion chamber muffler hybridized with multiple baffle plates will
be assessed.
In this paper, the acoustical model of the expansion chamber muffler will be
established by assuming that it is a rigid rectangular tube driven by a
piston along the tube wall. Using an eigenfunction (higher-order-mode
analysis), a four-pole system matrix for evaluating acoustic performance
(STL) is derived. To improve the acoustic performance of the expansion
chamber muffler, three kinds of expansion chamber mufflers (KA-KC) with
different acoustic mechanisms are introduced and optimized for a targeted
tone using a genetic algorithm (GA). Before the optimization process is
performed, the higher-order-mode mathematical models of three expansion
chamber mufflers (A-C) with various allocations of inlets/outlets and
various chambers are also confirmed for accuracy. Results reveal that the
STL of the expansion chamber mufflers at the targeted tone has been
largely improved and the acoustic performance of a reverse expansion
chamber muffler is more efficient than that of a straight expansion
chamber muffler. Moreover, the STL of the expansion chamber mufflers will
increase as the number of the chambers that separate with baffles
increases.
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