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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/3434

Title: Modeling and Performance Evaluation of a Simple Reactive Muffler of Vehicles Using CFD.
Authors: Abera, Dessalegn
Advisors: Dr.Ing Edessa Dribssa
Co-Advisor: Silesh Kore (PhD, Student)
Keywords: Transmission Loss
Back pressure
Insertion Loss
Copyright: Jan-2012
Date Added: 20-Jul-2012
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 and performance evaluation of a simple reactive muffler of vehicles using CFD. Simple expansion chamber muffler has been modeled numerically using Computational Fluid Dynamics (CFD) in order to determine its acoustic response. The CFD model consists of an axisymmetric grid with a single period sinusoid of suitable amplitude and duration imposed at the inlet boundary. The time history of the acoustic pressure and particle velocity is recorded at two points, one point in the inlet pipe and the other point in the outlet pipe. These time histories are 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 performance 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 upwind discretization was used for the density, momentum, energy, turbulent kinetic energy and turbulent dissipation rate equations. PISO pressure velocity coupling is used. The k-ԑ turbulence model was used for closure. The working fluid was air with the density modeled assuming an ideal gas. The boundary 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 expansion 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.
URI: http://hdl.handle.net/123456789/3434
Appears in:Thesis - Mechanical Engineering

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