Numerical Simulations of Aeroacoustic Fields around Automobile Rear-View Mirrors 2012-01-0586

A numerical method to simulate aeroacoustic fields around automobiles is proposed in the present paper. The proposed method can be used to compute sound emissions directly in both far fields and near fields. Sound passes through body structures near A-pillars and rear-view mirrors. The direct predictions of the sound to passengers therefore require solutions of acoustic near fields. Most aeroacoustics simulations around automobiles are based on Lighthill's analogy. Strictly speaking, Lighthill's analogy is not consistent in near fields because near fields are not governed by a simple wave equation. In the present paper, a proper approach is proposed to achieve further progress in the simulation of aeroacoustic fields around automobiles. The difficulties occur because the sound pressure is much smaller than the vortical flow pressure. The present method uses a flow/acoustics splitting technique that derives the modeled acoustic equations under the assumption that there is no acoustic feedback to the flows. The present acoustic equations are defined based on the difference between the compressible and incompressible flow equations. The acoustic equations are calculated with the fourth-order weighted essentially non-oscillatory scheme for the finite volume method, and a number of techniques are used to reduce the calculation time. These techniques use different meshes, time-step sizes, and computational regions in each flow and acoustics calculation. As a result, the present method makes it possible to simulate the acoustic near fields around the rear-view mirrors mounted on a vehicle. The acoustic fields for three different mirror shapes, namely, a baseline mirror, a mirror with a sharp edge around its stay, and a mirror with a sharp edge around its tip, are considered in the present paper. Consequently, the sound emissions from the mirrors and A-pillars are clearly visualized in the near fields as wall as the far fields, and differences in the acoustic fields among the mirror shapes are clarified.