A Correlation Study of Computational Techniques of a Three-pass Perforated Tube Muffler including Bem and 1d Methods

Automotive exhaust systems give a major contribution to the sound quality of a vehicle and must be properly designed in order to produce acceptable acoustic performances. Obviously, noise attenuation is strictly related to the internal gas-dynamic field that, on the other hand, needs to be optimised also in terms of pressure losses. In this work, the noise attenuation characteristics of a perforated muffler are investigated. Acoustic performances are specified at the component level as attenuation versus frequency (Transmission Loss), depending on the characteristics of the component itself. To this end different numerical analyses are employed. At first, a one dimensional simulation code (GT Power) is used to examine the influence of high temperature gas flow on the acoustic attenuation performance of the muffler, within the plane wave region. A more complex 3D FEM/BEM approach, is also realised using the VNOISE code, specifically designed for acoustic applications. Obviously, such analysis allows to obtain more accurate results at high frequency, hardly depending on the mesh size. Different flow velocities and gas temperatures are investigated, too. The Transmission Loss factor obtained from such approaches is, then, compared and the their potentiality and limitations are discussed.