A Coupled 1D-multiD Nonlinear Simulation of I.C. Engine Silencers with Perforates and Sound-Absorbing Material

Nowadays a great attention is paid to the level and quality of noise radiated from the tailpipe of intake and exhaust systems, to control the gas dynamic noise emitted by the engine as well as the characteristics of the cabin interior sound. The muffler geometry can be optimized consequently, to attenuate or remark certain spectral components of the engine noise, according to the result expected. Evidently the design of complex silencing systems is a time-consuming operation, which must be carried out by means of concurrent experimental measurements and numerical simulations. In particular, 1D and multiD linear/non-linear simulation codes can be applied to predict the silencer behavior in the time and frequency domain. This paper describes the development of a 1D-multiD integrated approach for the simulation of complex muffler configurations such as reverse chambers with inlet and outlet pipe extensions and perforated silencers with the addition of sound absorbing material. The 1D-multiD integrated approach is exploited to validate the transmission loss prediction of reverse chamber configurations with inlet and outlet extensions. Results have pointed out the capability of capturing transversal resonances at high and mid frequencies. Moreover a non linear approach is proposed to take into account the presence of the sound absorbing material into the conservation equations of a multidimensional solver. The properties of the sound absorbing material exploited have been taken form correlation adopted in the literature for 1D models. The momentum and energy conservation equations have been modified to take into account the interaction between the gas and sound absorbing material. Both the integrated 1D-multiD approach and the fully 3D model have been exploited for validation. The validation has been carried out considering two different geometries: an expansion chamber with an extended outlet pipe, with the sound absorbing material placed between the pipe extension and the canning, and a perforated pipe whose cavity has been completely filled with sound absorptive metallic wool. The results obtained both with the fully 1D analysis and the intergated approach are in agreement with the measured muffler preformances.