Acoustic Simulation of Vehicle Exhaust System using High Order Transfer Matrix Method Coupled with Finite Element Method 2014-32-0119

This paper addresses the numerical simulation of motorcycle exhaust system noise using a transfer matrix method (TMM) supporting high order analytical acoustic modes representation combined with finite element method (FEM) included in the Actran software, R15. In the state-of-the-art of hybrid TMM/FEM approach the main assumption consists in a 1D plane wave acoustic propagation in the components connections which is intrinsically limiting the maximum frequency of the analysis. In motorcycle exhaust systems this limitation is even stronger because typical geometries exhibit strong curvatures and bends causing the scattering of the acoustic wave into higher order modes. Therefore, results might be erroneous even at frequencies at which only the plane wave is expected to be propagating.

The improved transfer matrix method presented in this paper overcomes this limitation allowing to increase the range of applicability of this method. Specifically, the method is theoretically described and then validated on a set of test cases directly derived from a typical motorcycle exhaust system. Therefore, the method is validated on all the geometrical peculiarities that can be found in motorcycle exhaust networks such as strong bends and bifurcations. Results obtained by the TMM/FEM approach are compared with results provided by pure FEM modeling, in order to demonstrate the accuracy of the hybrid method.