針對一圓柱與壁面交界處，放置不同幾何參數之半圓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半圓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，並計算壁面剪應力以及渦度。在半圓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四種特徵模態，分別為「渦漩」、「不穩定渦漩」、「逆向流動」及「順向流動」。渦漩模態的流場特徵為數目為一或二的馬蹄形渦漩；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；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。使用適當設計的半圓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，雷諾數大約低於1000時，流場特徵結構為一源流且無渦旋逸放；在雷諾數大約高於1000時，流場特徵結構為一分歧線且出現渦旋逸放現象。最大剪應力發生在源流或分歧線與圓柱之間。在圓柱上游水平面上，依水平面的高度與馬蹄形渦漩中心點的相對位置而有不同的流體結構。若水平面切過馬蹄形渦漩中心點，則長時間之平均速度及流線圖中主要的流場特徵因受馬蹄形渦漩的影響而形成一四向鞍點與一源流。受半圓錐控制時，在「逆向流動」及「順向流動」兩個模態，因無馬蹄形渦漩，所以四向鞍點與源流也會消失。

Flow around juncture of a circular cylinder mounted normal to a flat plate modulated by a semi-cone installed around 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, wall shear stresses, and vorticity were calculated using the measured flow velocity data. Four characteristic flow modes (vortical flow, unsteady vortical flow, reverse flow, and forward flow) were observed in the domain of Reynolds number and semi-cone length at fixed semi-cone 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 semi-cone. No vortex shedding was observed in the cylinder wake near the wall at Reynolds numbers less than about 1000. At Reynolds numbers greater than about 1000, vortex shedding in the cylinder wake near the wall appeared. At Reynolds numbers less than about 1000, the time-averaged flow patterns in the near wake displayed a characteristic flow pattern of a source point, and the maximum wall shear stress appeared at a location between the source point and the cylinder. While at Reynolds numbers larger than about 1000, the time-averaged flow pattern in the near wake was featured by a bifurcation line, and the maximum wall stress was appeared between the bifurcation line and the cylinder.

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