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|Title: ||以被動流動控制方式調制鈍體流場特性及應用: 柵欄激擾|
Analysis and Application of Passive Flow Control on the Bluff-Body Flow Fields
|Authors: ||Chen-Wei Yang|
|Contributors: ||NTOU:Department of Mechanical and Mechatronic Engineering|
|Issue Date: ||2011-06-30T07:28:39Z
|Abstract: ||本研究將方柱置於風洞測試段，依雷諾數與旋轉角變化的關係，探討在不同自由流紊流強度下對方柱所造成的影響。透過低雷諾數煙線流場可視化及高雷諾數油膜流場可視化，觀察出在低雷諾數下對方柱的流場有三個不同行為特徵，分別為前緣分離流場模態、分離泡流場模態及邊界層貼附流場模態；在高雷諾數下對方柱的流場有四個不同行為特徵，分別為分離泡流場模態、分離流場模態、前緣分離流場模態及邊界層貼附流場模態。使用熱線風速儀，偵測方柱尾流區渦漩逸放之頻率做無因次化分析，獲得渦漩逸放頻率、史卓赫數及洛斯柯數隨雷諾數及自由流紊流強度變化的關係。最後，利用壓力掃瞄器擷取方柱表面的壓力分佈，再利用理論的計算得到升、阻力的分佈，進而探討在固定雷諾數下方柱之升、阻力隨不同自由流紊流強度下與方柱旋轉角變化的關係。結果顯示，當自由流紊流強度增加時，方柱之升、阻力係數會隨之降低，T.I. = 0.30%時，升、阻力係數最大值分別於旋轉角θ ＝ 45°及θ ＝ 12°；當T.I. > 0.30%時，升、阻力係數最大值皆發生於旋轉角θ ＝ 0°及θ ＝ 45°；T.I. = 0.75%時，升阻力不會再隨自由流紊流強度變化，趨於一定值。|
This study utilized a square cylinder installed in the test section of a wind tunnel. The effects of Reynolds number and rotation angle on the flow fields behind the square cylinder at different turbulence intensity were determined. The smoke-streak flow-field visualization scheme and the oil-flow visualization technique were utilized to visualization the flow structures at low and high Reynolds number, respectively. The flow structures at low Reynolds numbers were categorized into three patterns, that is, the leading-edge separation, separation bubble and boundary-layer attached flow modes. However, the flow structures at high Reynolds numbers were classified into four patterns, that is, the separation bubble, separation flow, leading-edge separation and boundary-layer attached flow modes. A hot-wire anemometer was installed in the wake to detect the vortex-shedding frequency. After a non-dimensional analysis, the relationships among the vortex shedding frequency, Strouhal number, Roshko number, and the free-stream turbulence intensity (T.I.) were determined. Furthermore, a pressure scanner was used to pick the surface pressure. The lift and drag were obtained using the pressure coefficient theorem. Additionally, the relationships among the Reynolds number, lift, drag and the free-stream turbulence intensity were determined. The experimental results shows that the lift and drag coefficients were lowered with increasing the free-stream turbulence intensity. The maximum lift coefficient and drag coefficient occurs at θ = 45° and θ = 12° for T.I. = 0.30%, respectively. The maximum lift coefficient and drag coefficient occurs at θ = 0° and θ = 45° for T.I. > 0.30%, respectively. However, the lift and drag coefficients were not varied with the free-stream turbulence intensity at T.I. = 0.75%.
|Appears in Collections:||[機械與機電工程學系] 博碩士論文|
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