Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/14853
標題: 垂直式消能池振盪流場之特性研究及應用PIV的可行性探討
Study on the characteristics of vertical drop structure and workable application of PIV
作者: 張勝淵
關鍵字: oscillation flow;垂直式消能池振盪流場
出版社: 土木工程學系
摘要: 
中 文 摘 要
本研究係利用水位計與二維光纖雷射杜普勒測速儀,針對單階垂直式消能池內之振盪流場進行定量量測實驗。在實驗之初,為了能夠清楚的掌握其水理之現象及瞭解流場振盪的機制與渦流消散增長之情形,在確認實驗段及上游流場之均勻性與穩定性後,遂使用高解析度具連拍功能之專業精密相機搭配雷射切光、鋁粉微粒之流場可視化方式,從模型構造較簡單的單階跌水工、具有設置尾檻之垂直式消能池、至具有自由液面之空穴流場等不同高度比(h/H)、尾檻長度對跌水池長度比(Ls/L)之模型佈置,作一定性觀察之實驗研究。定量量測方面,亦是在不同的模型尺寸下,改變不同的來流條件,以界定在不同之環境條件時各振盪流場發生之範圍。
在確定不同環境條件下各振盪流場發生之範圍後,遂選定一組在固定模型尺寸下,該振盪流場(過渡區流場、週期性振盪流場)發生振盪現象之相對臨界來流水深(Yc/H)範圍為最廣的實驗條件(此一實驗條件為:h/H = 0.43、Ls/L = 3.125、Yc/H = 0.181 ~ 0.238),將所量測之水位或速度時序列數據利用快速傅利葉轉換法進行頻譜分析,依據分析結果中主頻(f0)所對應的相對頻譜能量密度(Sη(f)、Su(f))之大小,來探討不同振盪型態流場之特性;並更進一步的從水位或速度時序列資料中判讀出流場之週期(T)、波高(Hw)及頻率(f)等物理量,透過統計的觀點對具明顯振盪特性之流場作一分佈趨勢之分析探討。
消能池內的振盪流場是一個夾帶大量氣泡與高度紊亂水流的流場,其中又以週期性振盪流場為最。應用質點影像測速儀於週期性振盪流場時,往往會因為氣泡反射脈衝雷射的強烈散射光,嚴重地影響拍攝畫面品質與分析結果之精確度,或甚至是損毀質點影像測速系統之數位感光鏡頭。因之,本實驗設計了一套以適當的光學濾片搭配螢光追蹤顆粒的光學濾波方法,希望對此一問題提供一個改善的方法,以利質點影像測速儀在週期性振盪流場的應用上有更高的實用性。
在使用光學濾波方法於週期性振盪流場的拍攝分析後,拍攝畫面品質並沒有因為強烈的散射光而有所影響,且質點影像測速系統之數位感光鏡頭亦無損壞。進一步的將所分析之結果,與並不使用光學濾波方法的可視化成果作一比對,發現分析之速度向量與鋁粉顆粒之拖痕長度有相當程度的符合。由此一結果可知,應用光學濾波方法於拍攝分析消能池內之週期性振盪流場上有很高的可行性。

ABSTRACT
The purpose of the present study is to make clear the characteristics of oscillation flows over two-dimensional vertical drop energy-dissipators, using fiber laser Doppler velocimeter (FLDV) and the wave gauge for quantitative measurement. In the preliminary study, flow visualization technique of aluminum particle tracking method was applied for qualitative observation. Under the condition of periodical and transitional oscillation flows, the model dimensions and the approaching-flow discharge were varied to determine the range of oscillation flows. Then, a special experimental condition, for which the approaching-flow discharge was most widespread, was selected for further analysis. Not only the fast Fourier transform method (FFT), but also the statistic methods were used to analyze the measuring data.
One of the special phenomena existing in the oscillation flows is that plenty of bubbles are entrained in the oscillation flows, especially the periodical oscillation flow. Due to the strong laser light scattered by bubbles, the image data captured by the particle image velocimetry (PIV) would be blurred. Moreover, the strong light might do damage to the optical sensor of PIV. In order to overcome this problem, the optical filtering method was proposed.
This innovative method could be operated by means of the optical filter and the fluorescent particles. Most of these corresponding experimental results were found to be in agreement with those of flow visualization observations. Therefore, such a problem could be improved efficiently by use of this method.
URI: http://hdl.handle.net/11455/14853
Appears in Collections:土木工程學系所

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