Modeling and Performance Evaluation of a Simple Reactive Muffler of Vehicles Using CFD
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Date
2012-01
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Addis Ababa University
Abstract
One of the components in the exhaust system of vehicle is muffler.
The purpose of the muffler is to
reduce the exhaust noise produced by the engine. The main objective of this study is modeling
performance evaluation of a simple
reactive muffler of vehicles using CFD.
Simple expansion chamber
muffler has been modeled numerically using Computational Flu
id Dynamics (CFD) in order to
determine its acoustic response. The CFD model consists of an ax
isymmetric grid with a single period
sinusoid of suitable amplitude and duration imposed at the inlet boundary.
The time history of the acoustic pressure and par
ticle velocity is recorded at two points, one point in
the inlet pipe and the other point in the outlet pipe. These time histories a
re Fourier transformed and
the Transmission Loss (TL) of the muffler is calculated. The mean flow has also been considered. The
mean flow model of the muffler is done using finer mesh and with
a suitable inlet velocity applied at
the inlet boundary and the pressure drop across the muffler is found. The performa
nce of the muffler is
evaluated based on Transmission Loss, Insertion Loss and Backpressure.
The simulation of the muffler was carried out using FLUENT software package. GAMBIT was used to
create a mesh and to define the boundary condition of
the required object, which is ready and analyzed
by FLUENT. The version used is FLUENT 6.3.26. The solver implemented was an axisymmetric,
segregated implicit solver with second order implicit time stepping. Second order upwin
discretization was used for the density, momentum, energy, turbulent kinetic energy and turbule
dissipation rate equations. PISO pressure velocity coupling is used. The k
-
for closure. The working fluid was air with the density modeled assuming an ideal gas. The bounda
conditions consist of a velocity inlet, a pressure outlet and a
series of walls. The CFD results are
compared with numerical results. Transmissions
Loss vs. frequency curves are analyzed.
Expansion chamber mufflers have been widely studied and results show that the larger the expan
ratio the greater the Transmission Loss. It is a good practice to design a muffler to work best in the
frequency range where the engine has the highest sound energy.
Description
Keywords
Transmission Loss (TL), Back pressure (BP), Insertion Loss (IL)