2nd Symposium on Fluid-Structure-Sound Interactions and Control Three-dimensional Wavelet Multi-resolution Analysis of Flow Structures behind a Vehicle External Mirror

The aerodynamic noise and vibration caused by the vehicle door mirror has been much studied [1], largely by numerical simulation [2]. It is evident that the aerodynamic noise and vibration are strongly associated with the flow structures, and the unsteady behavior of the vortex causes the wind noise. Recently the aero-acoustic characteristics of a vehicle door mirror were also studied by numerical simulation as well as experimental measurement [3]. Rinoshika et al. [4] experimentally investigated the flow structure around externally mounted vehicle mirror by the smoke-wire visualization technique and high-speed PIV technique. It is found that the length scales of separation region are generally insensitive to Reynolds number, and the size of vortices and the vorticity concentration increase with Reynolds number. Rinoshika and Watanabe [5] also applied one-dimensional wavelet multi-resolution technique to decompose Reynolds stress measured by high-speed PIV into various scales and analyzed the multi-scale flow structures behind a vehicle external mirror. But little attention has been paid to the analysis of the complex three-dimensional turbulent structures of various scales in the mirror wake from either the numerical or measurement data. To give further understanding of aerodynamic contribution to drag, noise and vibration, the detailed information on three-dimensional as well as multi-scale turbulent structures of mirror wake should be acquired, which it is important to design the shape of mirror having lower dynamic drag and noise. This is of fundamental significance and has not been previously investigated, thus motivating the present work. This work aims to apply the three-dimensional orthogonal wavelet multi-resolution technique to decompose the complex turbulent structures of the mirror wake into multi-scale structures based on the large eddy simulation and to provide both quantitative and qualitative information on the three-dimensional flow structures of various scales for designing the mirror with lower dynamic drag and noise.