Abstract
Part of vehicle interior noise is caused by the complex turbulent flow field behind the a-pillar and side mirror. It excites the structure of the side window, which radiates noise into the interior. Both aerodynamic pressure excitation and acoustic sound sources in the flow play an important role. In this work, the influence of both excitation mechanisms is investigated numerically in a hybrid simulation on a simplified car geometry. The generic model allows for an exact definition of boundary conditions and good reproducibility of simulation results. An incompressible Large-Eddy-Simulation (LES) of the flow is conducted, from which acoustic source terms within the flow field and transient fluid forces acting on the surface of the side window are extracted. This data is used in a coupled vibroacoustic and aeroacoustic simulation of the structure and passenger cabin of the vehicle. A finite element (FE) approach is used for the simulations and detailed modeling of the structure and the influence of interior absorption properties is emphasized. The computed excitation on the side window and the interior noise levels are successfully validated by using experimental data. The importance and contribution of both aerodynamic and acoustic pressure excitation to the interior sound level are determined.
Highlights
Reducing interior noise levels to improve driver and passenger comfort has gained increasing importance for researchers and acoustic engineers in the automotive industry
This study shows that it is possible to accurately determine the SPL inside a car model at an early stage in the development process
The incompressible, turbulent flow field is solved by the Computational Fluid Dynamics (CFD) software FASTEST-3D [16], which is based on a finite volume approach
Summary
Reducing interior noise levels to improve driver and passenger comfort has gained increasing importance for researchers and acoustic engineers in the automotive industry. The highly turbulent flow field in this area is characterized by velocity and pressure fluctuations with widely varying length scales. These fluctuations include sound sources present in the flow field and sound generated by the interaction of the flow with solid surfaces. A combination of acoustic pressure and aerodynamic wall-pressure fluctuations excite the flexible structure of the side window, leading to sound radiation into the interior. Both parts of the pressure differ in length scale, wave number, and energy content due to the disparity of scales. They cause different vibration characteristics of the structure, which will be examined in this work
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