研究生: |
張威力 Willy - Stevanus |
---|---|
論文名稱: |
不可壓縮垂直流經過有限長水平圓柱管的實驗研究 An experimental study on the vertical incompressible flow past a finite-length horizontal cylinder |
指導教授: |
林怡均
Yi-Jiun Peter Lin |
口試委員: |
陳明志
Ming-Zhi Chen 張倉榮 Cang-Rong Zhang 朱佳仁 Jia-Ren Zhu |
學位類別: |
碩士 Master |
系所名稱: |
工程學院 - 機械工程系 Department of Mechanical Engineering |
論文出版年: | 2013 |
畢業學年度: | 101 |
語文別: | 英文 |
論文頁數: | 166 |
外文關鍵詞: | Particle tracer flow visualization, Particle Image Velocimetry (P.I.V), Vortex shedding frequency, Fast Fourier Transform (FFT), Downwash effect. |
相關次數: | 點閱:291 下載:4 |
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The research studies the characteristics of the vertical incompressible flow past a finite-length horizontal cylinder in the near wake region with subcritical range of ReD from 250 to 1080. The experiments are performed in a vertical closed-loop water tunnel. Flow fields are observed by the particle tracer approach for flow visualization and measured by the Particle Image Velocimetry (P.I.V.) approach for velocity fields. The characteristics of vortex formation in the wake of the finite-length cylinder change at different regions from the tip to the base of it. Near the tip, a pair of vortices in the wake is observed and the size of the vortex increases as the observed section is away from the tip. Around a distance of 3 diameters of the cylinder from its tip, the vortex street in the wake is observed for some Reynolds numbers. The characteristics of vortex formation also change with Reynolds numbers. At X/D = -3, a pair of voctices is observed in the wake for ReD = 250, but as ReD increases to 560 the vortex street is observed at the same section. The vortex shedding frequency is analyzed by Fast Fourier Transform (FFT). Experimental results show that the downwash flow changes the vortex shedding frequency even to 5 diameters of the cylinder from its tip and vanishes about 10 diameters of the cylinder from its tip.
For the capped finite-length cylinder, flow visualization results show that the cap reduces the downwash effect. At X/D = -1, the vortex street is observed already at the lowest Reynolds number, ReD = 250. The vortex street is more
obvious as the observed section is away from the tip.
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