在一圓柱體與壁面交接處的上游，由於逆向壓力梯度與邊界層流動共同作用的結果，會產生馬蹄狀渦旋。這些馬蹄狀渦旋時常會在應用時造成負面的影響。本研究試圖探討一圓柱體與壁面交界處上游的流動特性以及兩種流動控制技術對這些馬蹄狀渦旋的影響。在一拖曳式水槽中，使用雷射光頁輔助質點軌跡可視化實驗方法，配合連續照相技術，探討圓柱與壁面交接處垂直對稱面與水平面之流體流動狀態，識別自然狀態流動以及加上流動控制設施後的流體特徵結構。結果顯示，在無加入流動控制設施時的自然狀態，一圓柱體與壁面交接處的上游，會依雷諾數與邊界層厚度的不同而產生一至三個馬蹄狀渦流。當在圓柱上游壁面附近加入安置一支小直徑的圓桿時，會在圓柱與小直徑圓桿之間引致數個渦流，無法消除馬蹄狀渦漩。若在圓柱體與壁面交界處安裝一個特殊設計的三角錐，則依三角錐的幾何參數(水平張角、垂直仰角、水平長度)與雷諾數的不同，會在圓柱上游區域三角錐的前端附近產生三種流體特徵結構：(1)渦流(vortical flow)、(2)逆流(reverse flow)、(3)順流(forward flow)。當產生「渦流」時，可能出現一或兩顆馬蹄狀渦流，顯示三角錐的設計未達效應；當產生「順流」時，顯示馬蹄狀渦流已完全被消除；當產生「逆流」時，流場的結構是介於「渦流」與「順流」之間的過渡狀態。所以，如果將三角錐的幾何參數調整在「順流」模態時，即可以達到消除馬蹄狀渦流的目的。

The flow around the upstream area of the juncture of a wall and an obstacle extruding from the wall may present interesting vortical flow structure which was commonly termed the horseshoe or necklace vortices. The vortical flow structure usually induced negative effects in the applications such as the heat transfer efficiency of heat exchangers, scour of river bed for the bridge columns, aerodynamic performance of wings, etc. There was a necessity to eliminate the vortical flow structure around the obstacle/wall juncture. This study focused on characterizing the effects of two flow control technologies on the flow characteristics upstream the circular cylinder/flat plate juncture. The laser-light-sheet flow visualization technique and the time-evolving photographing method were employed to obtain the dynamic images of flow patterns. The first method was the rod-control method—a small circular rod placing horizontally in front of the juncture. The second method was the upstream filling method—a pyramid-shaped small block was installed at the juncture. The rod-control method was proved ineffectively in eliminating the horseshoe vortices. Three characteristic flow patterns (vortical flow, reverse flow, and forward flow) appeared when the pyramid block was installed, depending on the geometric configurations and dimensions of the pyramid block as well as the Reynolds number. Operating the pyramid block in the vortical flow regime, the horseshoe vortical flow structure still existed. Operating the pyramid block in the forward flow regime, the horseshoe flow structure was completely eliminated. The reverse flow regime was a status for transition from the vortical flow regime to forward flow regime.

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