CFD Investigation of the Effect of Fluid-Structure Interaction on the Transmission Loss of ICE Silencers

In the last decades numerical simulations have become reliable tools for the design and the optimization of silencers for internal combustion engines. Different approaches, ranging from simple 1D models to detailed 3D models, are nowadays commonly applied in the engine development process, with the aim to predict the acoustic behavior of intake and exhaust systems. However, the acoustic analysis is usually performed under the hypothesis of infinite stiffness of the silencer walls. This assumption, which can be regarded as reasonable for most of the applications, can lose validity if low wall thickness are considered. This consideration is even more significant if the recent trends in the automotive industry are taken into account: in fact, the increasing attention to the weight of the vehicle has lead to a general reduction of the thickness of the metal sheets, due also to the adoption of high-strength steels, making the vibration of the components a non negligible issue. In this work, a CFD compressible solver capable to describe the fluid-structure interaction problem has been implemented and validated. The approach is based on the adoption of two different domains for the solution of the governing equation for the fluid and for the structure. At each time-step, the pressure field computed on the fluid domain is used as an input for the solution of the displacement of the structure. A mesh motion strategy is adopted, for both the fluid and solid domain, in order to describe the deformation of the walls. The solver has been applied for the simulation of the acoustic behavior of a simple expansion chamber, considering different wall thickness, in order to investigate the effect of the structure vibration on the transmission loss. Results have been validated resorting to experimental measurements available in the literature.