Cálculo acústico de silenciadores de escape con arrays de conductos mediante elementos finitos

Abstract

The aim of this project is to determine and analyze the transmission loss (TL), this means the acoustic attenuation, due to the different geometrical configurations of our chamber from an exhaust system of an internal combustion engine. The main function of silencers is the attenuation of the flow pulsations generated by the discharge gases process in the internal combustion engine. This study will be performed using Finite Element Methods (FEM) programs, which is a mathematical technique for finding approximate solutions to boundary value problems for partial differential equations. The aim of the development and use of this type of programs is based on the reduction of time and also the economic advantage, compared to the conventional measurement techniques. It has been also developed simple analytical techniques (plane wave’s models), which can be applied during the design stage, to be able to establish a first approximation of the behavior of our silencer under study. The main disadvantage of this technique is the type of geometric design which can be studied. This means, it is too complicated to study with this technics, complex designs. For this reason, we have use a Finite Element Method (FEM) which permit the study of a more complex geometry. In reference to the Finite Element Method (FEM), in this project we have use two different programs to be able to determine whether the design is optimal or not. These programs are Ansys and Sysnoise. Ansys is used to design the geometry and to establish the mesh on our device (Preprocessor) and with Sysnoise, we establish the pressure behavior and velocity behavior of our device (Postprocesor). With these results we are able to analyze the transmission loss (TL) of our silencer and determine whether the design is optimal or not, depending on our initial criterion. We must say that Ansys is a powerful program with which we could also study the acoustic behavior of our devices. However, Sysnoise is not only more specialized, but also requires a less computational effort, this translate in a more efficient and economic analysis. There are lots of different geometric configurations to reach an optimal sound attenuation of the exhaust system, in the case of an internal combustion engine. In this project we will focus on the study of the transmission loss (TL), acoustic attenuation, of two different geometrical configurations of our silencer. The first device under study will be a non-axisymmetric (rectangular) empty chamber and an axisymmetric (circular) empty chamber configuration and the second device under study will be a non-axisymmetric chamber and an axisymmetric chamber with radial and axial Arrays configuration.