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題名 | Phase-Resolved Investigation of Vortex Shedding in Flow Past a Circular Cylinder by Using Laser Doppler Anemometry=雷射都卜勒流速儀於圓柱尾流相位解析流場之研究 |
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作者 | 李文宗; 吳聖俊; 陳瑤明; Lee, Wen-tsung; Wu, Sheng-jiun; Chen, Yau-ming; |
期刊 | 中國機械工程學刊 |
出版日期 | 19981000 |
卷期 | 19:5 1998.10[民87.10] |
頁次 | 頁465-473 |
分類號 | 446.11 |
語文 | eng |
關鍵詞 | 雷射都卜勒流速儀; 圓柱尾流; 相位解析流場; Phase average; Vortex shedding; Near wake; LDA; |
中文摘要 | 本文利用雷射流速儀及相位平均法,來研究流經圓柱尾流的渦流剝離現象,及剝 離後渦流的運動行為。 以圓柱直徑為參考長度計算所得的雷諾數為 1750。藉由速度相位參 考源,可將渦流剝離期間的週期流場重建,並由計算固定相位的渦度值,可探討渦流運動的 特性,並且找出流場的臨界點。而藉由三項速度解析的方法,可分析由渦流週期運動所引起 的雷諾應力及局部紊流的雷諾應力分佈。由實驗結果顯示,渦流在未剝離期間以 0.51 倍的 平均速度往下游運動,而剝離後則以 0.82 倍的平均速度往下游運動。另外由比較週期雷諾 正向應力與局部紊流的雷諾正向應力比較發現,主流方向的週期雷諾正向應力 (uu) 遠小於 其他的電諾正向應力 (<u' u'>),v v,<v' v'>)。 在渦流完全剝離的區域,渦度極大值的位 置所對應的為週期正向應力的極小值的位置。相反的,渦度極大值的位置與隨機紊流正向雷 諾應力的極大值位置重合。 |
英文摘要 | This paper describes an experimental investigation of near wake flow behind a circular cylinder. The Reynolds number, based on the diameter of the circular cylinder, was found to be 1750. Conditional sampling and phase averaging techniques together with laser-Doppler anemometry were employed in the experiment. The kinematics of vortex-formation process is described in terms of the formation and evolution of saddle points between vortices in the near wake. Using phase vorticity, the detailed characteristics of vortex motion and downstream variations of vortex can be examined. The celerity of a vortex in the base region is found to be 0.52U0. After a vortex sheds completely, its celerity becomes 0.82U0. In addition, the Reynolds normal stresses, which are caused by periodic and random motions at different phases, were also explored. The Reynolds normal stress (u u) produced by periodic motion in streamwise direction is insignificant in magnitude, while the other Reynolds normal stresses (<u' u'>), v v,<v' v'>) are important because their quantities are larger. When a vortex structure becomes well defined, vorticity peaks are located in regions where the Reynolds normal stresses of periodic components are small. On the contrary, the peaks of vorticity coincide with the peaks of Reynolds normal stresses, which are caused by local turbulent fluctuation. |
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