Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/14097
標題: 方形體上方圓錐形渦流流場特性之實驗研究
Experimental Study on the Characteristics of Conical Vortices over a Flat Roof
作者: 賴葦帆
Lai, Michael
關鍵字: conical vortex
流場可視化
flow visualization
PIV
圓錐形渦流
質點影像測速儀
出版社: 土木工程學系
摘要: 本文旨在運用流場可視化法,對於與水流方向具45度夾角之方形體上方圓錐形渦流流場,探討在不同雷諾數之條件下(雷諾數介於6000 ~ 30000之間),會形成何種不同型態之流場結構,並據其特徵作定性之描述。研究中並特別針對雷諾數分別為30000以及6000兩者流況明顯不同之情形,以先進之質點影像測速儀(Particle Image Velocimetry , 簡稱PIV)系統進行相關的定量分析研究。 於定性之觀察結果中發現,此圓錐形渦流流場因雷諾數的改變而產生明顯的變化。當雷諾數為30000、24000、18000時,圓錐形渦流乃屬成對出現;但當雷諾數降至12000、6000,渦流不再成對出現而僅出現於一側,且不固定出現於左側或右側。 定量之量測分析結果中,對雷諾數為30000及6000時之渦心軌跡線,於分別使用煙線相片分析與PIV分析結果之差異性加以說明比較。另外對於不同橫截面上之渦流強度及其變化情形也一併加以探討。經由本文對於方形體上方圓錐形渦流流場運動情形之探討,其結果可供日後相關研究參考。
When an uniform flow encounters an oblique building with square cross-section, a three-dimensional flow field, so called conical vortex, is formed above the roof of the building. The flow structure and characteristics of the conical vortex were studied experimentally by using two flow visualization techniques and particle image velocimetry (PIV). The Reynolds numbers (Re), based on the free stream velocity (U0) and the edge length of the roof (D), range from 6000 to 30000. The purpose of the present study is to provide the qualitative and quantitative properties of the conical vortex. By lowering the Reynolds number from 30000 to 6000, the flow field structure of the conical vortex was observed by flow visualization methods and found to appear a distinct change. The conical vortex appeared in a pair when Re=18000、24000、 30000 and only on one side when Re=6000、12000. With regard the conditions for the Reynolds numbers are 6000 and 30000, detail characteristics of the conical vortex behavior, including the position of vortex core line and the vortex strength varies with different transverse cross-section, are quantified and discussed in the present study.
URI: http://hdl.handle.net/11455/14097
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