CFD investigation of a generic vehicle side-view mirror

Abstract

Electric automobiles are becoming more common in today’s society. Since interior car noise can have negative mental health effects for the driver and passengers, it becomes relevant to find out how it is being generated. One important source of noise is the surface pressure fluctuations caused by shear layer impingement and turbulence from the flow around a side-view mirror. Even though many studies about the flow past a side-view mirror have been done, there is not sufficient research for lower speed cases at which electric cars drive at. The purpose of this project is therefore to study the flow around a generic side-view mirror and investigate how it generates noise for some of these cases. The computational fluid dynamics (CFD) software STAR-CCM+, running both steady and unsteady Reynolds-Averaged Navier Stokes (RANS) simulation models is used. Three cases at different freestream speeds of 20, 30 and 40 m/s are simulated. To ensure accurate results, a mesh independence study is carried out for the 40 m/s case with steady RANS simulation. The final mesh is then used to simulate the 20 and 30 m/s cases as well. The steady flow fields were obtained using the realizable k −" model and later used as initialization fields for the unsteady cases, were SST k − ! model is used. Pressure fluctuations data series of specific sensors placed on the surfaces of the mirror and window where analyzed for their power spectral density (PSD) in the frequency domain. For sensors placed in the back of the mirror and on the window inside the recirculation region, noticeable peaks at 500-1300 Hz in the signal’s power were observed. Comparison of the PSD’s against the Strouhal number revealed that the power peaks are due to coherent structures in the free shear layer developed from the mirror edges. Those PSD peaks will generate tonal noise which is of 500-1300 Hz. Measures should be taken to prevent drivers and passengers from hearing this kind of noise. The present study is also a fundamental step to provide hydrodynamic pressure fluctuation data for a future acoustic wave simulations.