針對一圓柱與壁面交界處，放置不同幾何參數之三角錐於圓柱與壁面上游交界處，在一拖曳式水槽中使用實驗方法來探討受三角錐控制之圓柱與壁面交接處上游與下游的流場特徵。使用雷射光頁輔助質點軌跡法觀察流場圓柱與壁面交接處上游與下游的垂直對稱面與水平面的特徵行為，再藉由質點影像測速儀量測速度場，轉換為流線，並計算壁面剪應力。在三角錐長度與雷諾數的域面上，圓柱與壁面上游交界處的流場呈現五種特徵模態，分別為「渦漩」、「不穩定渦漩」、「逆向流動」、「過渡」及「順向流動」。渦漩模態的流場特徵為數目固定的馬蹄形渦漩；不穩定渦漩模態的流場特徵呈現數目不固定的馬蹄形渦漩；逆向流動模態時，靠近壁面處流體呈現逆向流動的行為；過渡模態時，靠近壁面處的流體隨機出現逆向流動或順向流動。順向流動模態時，靠近壁面處流體呈現順向流動的行為。當圓柱上游形成馬蹄形渦漩時，最大剪應力產生在馬蹄形渦漩處。使用適當設計的三角錐可消除圓柱上游的馬蹄形渦漩，降低壁面剪應力，因而改善馬蹄形渦漩對圓柱根部的沖刷效應。在圓柱尾流垂直面上，雷諾數低於1000時，流場特徵結構為一源點；在雷諾數高於1000時，流場特徵結構為一分歧線。最大剪應力發生在源點或分歧線與圓柱之間。在圓柱下游水平面上，長時間之平均速度及流線圖中主要的流場特徵為兩顆反向旋轉之渦漩。分析尾流區流速隨時間之變化，研究不同流場模態對尾流渦漩逸放頻率之影響，發現接近圓柱底部之水平面上觀察不到渦漩逸放之現象。

Flow around juncture of a circular cylinder mounted normal to a flat plate modulated by a tetrahedron installed around the upstream corner of the cylinder were investigated experimentally in a water towing tank. The flow patterns were studied by particle-tracking flow visualization method. The flow velocities were measured by particle image velocimetry (PIV). The streamlines and wall shear stresses were calculated using the measured flow velocity data. Five characteristic flow modes (vortical flow, unsteady vortical flow, reverse flow, transition flow, and forward flow) were observed in the domain of Reynolds number and tetrahedron length at fixed tetrahedron angles. Horse-shoe vortices wrapping from the upstream region and extending to the downstream area of the circular cylinder appeared in the vortical flow mode. Flow went upstream was found in the reverse flow mode. Smooth flow went downstream without any vortices or reverse flow were observed in the forward flow mode. The calculated wall shear stresses showed peak values at the locations of vortices. The reverse and forward flow modes did not present large local wall shear stresses, which denoted a success of flow control by the tetrahedron. At low Reynolds number (e.g., 500), no vortex shedding was observed in the wake near the wall. At mid and high Reynolds numbers (e.g., 1600, 2500, 5000), regular vortex shedding with a Strouhal number about 0.2 appeared in the wake near the wall.

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