Development of an Air Intake System Using Vibro-Acoustics Numerical Modeling 2001-01-1519

This paper describes the use of Vibro-Acoustics numerical modeling for prediction of an Air Intake System noise level for a commercial vehicle. The use of numerical methods to predict vehicle interior noise levels as well as sound radiated from components is gaining acceptance in the automotive industry [1]. The products of most industries can benefit from improved acoustic design. On the other hand, sound emission regulation has become more and more rigorous and customers expect quieter products. The aim of this work it is to assess the Vibro-Acoustics behavior of Air Intake System and influence of it in the sound pressure level of the vehicle. Analyses were performed using the Finite Element Method (FEM) and Boundary Element Method (BEM), specifically the following analyses were done: normal acoustic modes, transfer function with Structure Fluid Interaction (SFI) and without (SFI), acoustic radiation and study of order with verification of frequencies influence of the engine rotation on the evaluation of sound pressure level [2,3,4]. The main frequencies that influence Vibro-Acoustics behavior of the air system were checked. For the commercial vehicle with 5 cylinders engine, a sweeping from 0 to 350 Hz was done, aiming on verifying the influence of the generated sound pressure level with respect to the engine rotating frequency, i.e., 2^nd 1/2 order at 175 Hz and 4200 rpm engine peak rotation, and 5^th order at 350 Hz. The results have shown that there is a big potential to influence the radiated sound pressure level (at high frequencies) for the areas represented by the intake duct, medium duct and air filter. This is mainly due to the high flexibility of the material used. Overall, the acoustic analyses have shown that an increase in stiffness on this zone can reduce the acoustic energy emitted to the exterior. As a conclusion, the use of the Helmholtz Resonators [5,6] close to the turbine region have been suggested to reduce the sound pressure level in air intake system when sized for specific frequencies, as for example in the range between 50 to 100 Hz, which was verified in the analyses.