Experimental investigation of freely falling thin disks. Part 1. The flow structures and Reynolds number effects on the zigzag motion
| Autor: | Hongjie Zhong, Shiyi Chen, Jiezhi Wu, Cunbiao Lee, Zhuang Su, Mingde Zhou |
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| Rok vydání: | 2013 |
| Předmět: | |
| Zdroj: | Journal of Fluid Mechanics. 716:228-250 |
| ISSN: | 1469-7645 0022-1120 |
| DOI: | 10.1017/jfm.2012.543 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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