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 used materials and to its
internal geometry. This last influences the wave propagation and
the gas-dynamic field.
The purpose of this paper is to describe advantages and
disadvantages of different numerical approaches in evaluating the
acoustic performance in terms of attenuation versus frequency
(Transmission Loss) of a commercial two perforated tube muffler
under different conditions.
At first, a one-dimensional analysis is performed through the 1D
GTPower® code, solving the nonlinear flow equations which
characterize the wave propagation phenomena. The muffler is
characterized as a network of properly connected pipes and volumes
starting from 3D CAD information.
Then, two different 3D analyses are performed within the
commercial STS VNOISE® code. The first one assumes rigid wall
hypothesis. In the second, a preliminary FEM modal analysis of the
structure is realized. The computed structure natural frequencies
are then imported in the BEM model in order to carry out the
complex fluid-structure interaction. The effects of this last
condition on TL calculation are compared and discussed. In
addition, both flow and temperature effects have been included in
the modeling and discussed with the previous analyses. Agreement
among these numerical evaluations and related limitations are put
into evidence for different configurations.