Wavelet multi-resolution analysis on wake flows behind three-dimensional bluff bodies

Abstract

In order to improve the aerodynamic performance of external side mirror of race car, the wake flow around three-dimensional bluff body is studied in this study. Firstly, the high-speed PIV was applied to measure turbulent wakes generated by asymmetric side mirror (called CT-cylinder) and semi-cylinder at a Reynolds number of 6,240 in the circulating water channel. These flow fields were evaluated by time-averaged, instantaneous and phase-averaged flow structures and the FFT analysis. And then, one-and two-dimensional wavelet multi-resolution techniques were used to analyze the instantaneous velocity and vorticity data in order to obtain the turbulent structures of various scales. It is found that the CT-cylinder generates smaller separation region and lower Reynolds shear stresses than that of semi-cylinder, and produces the asymmetric flow structure and aerodynamic downforce. In the wake of CT-cylinder, the size or shape of the vortices shed from upper and lower side is different and the vorticity of upper side is larger than that of lower side, causing asymmetry and high-intensity vertical velocity fluctuation. The most contribution to the Reynolds shear stress come from large-scale structures and account about 82.0 % for CT-cylinder wakes and 78.6 % for semi-cylinder wake. The relatively small-scale structures make less contribution to Reynolds shear stresses.