One of the components in the exhaust system of vehicle is muffler.rn The purpose of the muffler is to rnreduce the exhaust noise produced by the engine. The main objective of this study is modelingrnperformance evaluation of a simplern reactive muffler of vehicles using CFD.rn Simple expansion chamber rnmuffler has been modeled numerically using Computational Flurnid Dynamics (CFD) in order to rndetermine its acoustic response. The CFD model consists of an axrnisymmetric grid with a single period rnsinusoid of suitable amplitude and duration imposed at the inlet boundary. rn rnThe time history of the acoustic pressure and parrnticle velocity is recorded at two points, one point in rnthe inlet pipe and the other point in the outlet pipe. These time histories arnre Fourier transformed and rnthe Transmission Loss (TL) of the muffler is calculated. The mean flow has also been considered. Thernmean flow model of the muffler is done using finer mesh and withrn a suitable inlet velocity applied at rnthe inlet boundary and the pressure drop across the muffler is found. The performarnnce of the muffler is rnevaluated based on Transmission Loss, Insertion Loss and Backpressure. rnThe simulation of the muffler was carried out using FLUENT software package. GAMBIT was used torncreate a mesh and to define the boundary condition ofrn the required object, which is ready and analyzed rnby FLUENT. The version used is FLUENT 6.3.26. The solver implemented was an axisymmetric,rnsegregated implicit solver with second order implicit time stepping. Second order upwinrndiscretization was used for the density, momentum, energy, turbulent kinetic energy and turbulerndissipation rate equations. PISO pressure velocity coupling is used. The krn-rnrnrnrnfor closure. The working fluid was air with the density modeled assuming an ideal gas. The boundarnconditions consist of a velocity inlet, a pressure outlet and arn series of walls. The CFD results are rncompared with numerical results. Transmissionsrn Loss vs. frequency curves are analyzed.rn rnExpansion chamber mufflers have been widely studied and results show that the larger the expanrnratio the greater the Transmission Loss. It is a good practice to design a muffler to work best in thernfrequency range where the engine has the highest sound energy.