The main objective of this study is to use CFD tool to obtain the perforate impedance data. No restrictions on the flow and acoustic modeling are placed. The input to the muffler flow model is a turbulent velocity profile. An unsteady flow analysis is carried out to predict the pressure and velocity fluctuations at various locations in the muffler. The impedance is then calculated for different frequencies of input fluctuations and compared with existing empirical models. Transmission Loss calculations are also carried out. The effects of mean flow Mach number and porosity on impedance are investigated. The results indicate that this technique holds promise and can be a good design tool for complex geometries.