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Experimental investigation of freely falling thin disks. Part 1. The flow structures and Reynolds number effects on the zigzag motion

  • Hongjie Zhong (a1) (a2), Cunbiao Lee (a1), Zhuang Su (a1), Shiyi Chen (a1), Mingde Zhou (a1) and Jiezhi Wu (a1)...


This paper describes an experimental investigation of the dynamics of a freely falling thin circular disk in still water. The flow patterns of the disk zigzag motion are studied using dye visualization and particle image velocimetry. Time-resolved disk motions with six degrees of freedom are obtained with a stereoscopic vision method. The flow separation and vortex shedding are found to change with the Reynolds number, $\mathit{Re}$ . At high Reynolds numbers a new dipole vortex is shed that is significantly different from Kármán-type vortices. The vortical structures are mainly composed of leading-edge vortices, a counter-rotating vortex pair and secondary trailing-edge vortices. The amplitude of the horizontal oscillation is also dependent on the Reynolds number with a critical Reynolds number ${\mathit{Re}}_{cr} \approx 2000$ , where the oscillatory amplitude is proportional to $\mathit{Re}$ for $\mathit{Re}\lt {\mathit{Re}}_{cr} $ , but becomes invariant for $\mathit{Re}\gt {\mathit{Re}}_{cr} $ . Three-dimensional dipolar vortices were also observed experimentally.


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