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研究生： 林柏豪
Bo-hao Lin
論文名稱： 二維方柱之流場與動態渦漩研究
Flow and Vortex Shedding of Two-Dimensional Square Cylinder
指導教授： 黃榮芳
Rong-fang Huang
口試委員: 張家和
Chia-ho Chang
劉昌煥
Chang-huan Liu
楊騰芳
Ten-fang Yang
孫珍理
Chen-li Sun
陳明志
Ming-chih Chen
唐永新
Yung-hsin Tang
葉啟南
Chi-nan Yeh
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： 2007
畢業學年度： 95
語文別： 中文
論文頁數： 247
中文關鍵詞： 方柱 、表面流場 、渦漩逸放
外文關鍵詞： square cylinder, surface flow pattern, vortex shedding
相關次數： 點閱：423  下載：5 
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    • 本研究針對無傾角之二維方柱，探討雷諾數與旋轉角的變化對方柱表面流場、壓力分佈、升阻力特性以及尾流區渦漩逸放之流場結構的影響。在一氣動力風洞中，藉由煙線可視化技術(低雷諾數區域)與表面油膜流法(高雷諾數區域)觀察方柱表面流場的特徵，並利用質點影像速度儀量測方柱周圍的速度場，分析方柱四個面表面流體流動的特徵模態，同時利用表面拓樸分析得到表面流場時間平均流形的特徵模型。使用表面壓力孔與壓力掃描技術量測方柱表面的壓力分佈，並計算升、阻力係數，同時探討壓力分佈與表面流場特徵的相關性。使用熱線風速儀量測方柱尾流區動態結構的頻率、統計紊流特性與尾流寬度，並將結果與表面流場特徵態相結合。方柱表面流場的特徵模態與旋轉角有緊密的相關性，依表面與旋轉角的不同，可觀察到方柱側面呈現雙分離泡、單分離泡與貼附邊界層三種模態；方柱下風面呈現迴流泡與單分離泡兩種模態。當旋轉角為15度時，方柱兩側面的流場特徵模態由雙分離泡轉換為單分離泡，下風面的流場特徵模態由迴流泡轉換為單分離泡。在旋轉角15度時升力與阻力係數降到最低值，分別為 -0.87與1.56。根據熱線風速儀輸出的時序圖及所對應的頻譜圖，尾流區渦漩逸放之特徵為超臨界模態，顯示紊流加附在週期振盪訊號上的份量頗強。在旋轉角15度時，表面流模態轉換，造成表面流部份貼附，使得尾流寬度達到最窄，故其渦漩逸放頻率最高，因而史卓數達到最大值，也因而導致阻力係數達到最小值。很明顯的，方柱表面流場的特徵模態主導了表面壓力分佈與尾流渦漩逸放的特性。

    The surface flow characteristics, pressure distribution, lift/drag variation, and wake instability of a two-dimensional finite square cylinder are experimentally investigated in a wind tunnel. The cross-sectional profile of the square cylinder is 6 cm × 6 cm and the aspect ratio of the finite square cylinder is 8.8. The surface flows are studied by using the smoke-wire and surface oil-flow techniques at low and high Reynolds numbers, respectively. The particle image velocimeter is employed to obtain quantitative, time-evolving flow structures. Topological flow analysis is presented to delineate the surface flow patterns. The surface pressures are measured by the pressure tapes in conjunction with a home-made pressure scanner. The lift and drag coefficients are calculated by using the measured surface pressure data. The wake instability frequency and statistical turbulence properties are probed by a hot-wire anemometer. It is found that the surface flow patterns are closely related to the inclined angle of the cylinder. The lateral surfaces of the square cylinder present three characteristic flow modes: dual bubble, single bubble, and attached boundary layer. While the recirculation bubble and single bubble modes can be observed on the lee-side surface. The characteristic flow patterns of the lateral surfaces change from dual bubble to single bubble and that of the lee-side surface evolves from recirculation bubble to single bubble at the inclined angle of about 15 degree. At this critical inclined angle, the lift and drag coefficients attain the minimum values and the Strouhal number reaches a maximum because the wake width is reduced to a minimum due to the change of the characteristic modes of surface flow. It can be concluded that the surface pressure distribution, lift/drag coefficients, and wake characteristics are dramatically affected by the surface flow patterns which are drastically dominated by the cylinder inclined angle and Reynolds number.

    摘要……………………………………………………………………… i Abstract………………………………………………………………… ii 誌謝……………………………………………………………………… iii 目錄……………………………………………………………………… iv 符號索引………………………………………………………………… vii 表圖索引………………………………………………………………… x 第一章 緒論…………………………………………………………… 1 1.1 研究動機………………………………………………………… 1 1.2 文獻回顧………………………………………………………… 2 1.2.1 圓柱之流場特性……………………………………… 2 1.2.2 平板之流場特性……………………………………… 3 1.2.3 矩形柱與方注之流場特性…………………………… 5 1.3 研究目標………………………………………………………… 8 第二章 研究構思及實驗設備、儀器與方法…………………………………………… 9 2.1 研究構思………………………………………………………… 9 2.2 實驗設備………………………………………………………… 10 2.2.1 風洞…………………………………………………… 10 2.2.2 方柱模型……………………………………………… 12 2.3 實驗儀器及方法………………………………………………… 13 2.3.1 自由流速的偵測……………………………………… 13 2.3.2 煙線流場可視化……………………………………… 14 2.3.3 表面油膜流法………………………………………… 17 2.3.4 壓力掃描器…………………………………………… 24 2.3.5 質點影像速度儀(PIV)……………………………… 25 2.3.6 尾流渦漩逸放頻率的偵測…………………………… 27 Part I. 高雷諾數之表面流與壓力特性 第三章 表面流特性……………………………………………………………………… 28 3.1 方柱A面之流場…………………………………………………… 28 3.2 方柱B面之流場…………………………………………………… 29 3.2.1 流場特徵模態………………………………………… 29 3.2.2 邊界層分離、再接觸及分離泡的行為與特性……… 31 3.3 方柱C面之流場…………………………………………………… 32 3.3.1 流場特徵模態………………………………………… 32 3.3.2 邊界層分離、再接觸及分離泡的行為與特性……… 34 3.4 方柱D面之流場…………………………………………………… 35 3.4.1 流場特徵模態………………………………………… 35 3.4.2 停滯流、邊界層分離、再接觸及迴流泡的行為與特 36 3.5 方柱流場拓樸分析………………………………………………… 37 第四章 表面壓力分佈與升阻力特性……………………………………………………… 42 4.1 方柱表面壓力分佈………………………………………………… 42 4.1.1 方柱A面壓力分佈……………………………………… 42 4.1.2 方柱B面壓力分佈……………………………………… 43 4.1.3 方柱C面壓力分佈……………………………………… 44 4.1.4 方柱D面壓力分佈……………………………………… 45 4.1.5 雷諾數對方柱表面壓力之影響……………………… 46 4.2 方柱表面升阻力特性……………………………………………… 46 Part II. 低雷諾數之流場特性 第五章 煙線流場特徵……………………………………………………………………… 49 5.1 方柱周圍流場之特徵模態………………………………………… 49 5.2 方柱尾流區之剪流層行為………………………………………… 51 5.3 方柱停滯流之特性………………………………………………… 52 第六章 PIV量測之量化流場……………………………………………………………… 53 6.1 不同樣本平均次數之速度向量流線圖…………………………… 53 6.1.1 方柱旋轉角α = 0deg………………………………… 53 6.1.2 方柱旋轉角α = 7deg………………………………… 55 6.1.3 方柱旋轉角α = 22deg………………………………… 56 6.1.4 方柱旋轉角α = 45deg………………………………… 58 6.1.5 穩態紊流場分析……………………………………… 59 6.2 瞬時流場之衍化過程……………………………………………… 60 6.2.1 速度向量流線圖……………………………………… 60 6.2.2 紊流強度分佈………………………………………… 64 6.2.3 紊流動能分佈………………………………………… 65 6.3 平均流場…………………………………………………………… 66 6.3.1 速度向量流線圖……………………………………… 66 6.3.2 渦度、紊流強度與紊流動能分佈…………………… 67 6.3.3 速度與之量化分析…………………………………… 69 6.3.4 紊流強度之量化分析………………………………… 70 6.3.5 紊流動能之量化分析………………………………… 73 6.3.6 拓樸分析……………………………………………… 75 6.4 剪流層分析………………………………………………………… 76 Part III. 方柱尾流區渦漩逸放 第七章 渦漩逸放的頻率與尾流寬度……………………………………………………… 78 7.1 尾流區渦漩逸放之頻率特性……………………………………… 79 7.2 尾流寬度…………………………………………………………… 82 第八章 統計上的特性……………………………………………………………………… 84 8.1 概率密度函數……………………………………………………… 84 8.2 相關性係數………………………………………………………… 85 8.3 特徵長度尺度……………………………………………………… 87 第九章 結論與建議………………………………………………………………………… 88 9.1 結論………………………………………………………………… 88 9.2 建議………………………………………………………………… 90 參考文獻…………………………………………………………………………………… 91

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