剪切流通過圓柱之渦流流洩及抑制之研究

VORTEX SHEDDING AND ITS SUPPRESSION FOR A SHEAR FLOW PAST A CIRCULAR CYLINDER

In the present study, we investigated computationally the laminar Couette flow past a periodically rotating circular cylinder for the purpose of observing flow phenomena behind the cylinder and controlling vortex shedding. The cylinder was placed with its center on the centerline. The Reynolds number, based on the mean incoming velocity and the width between the two flat plates, was fixed at 250. The unsteady laminar flow was computed via a finite volume method with an implicit time-marching technique. The two main parameters which affect the flow development behind the cylinder are the period (T), and the peak rotation speed (A) of the cylinder under rotation. We studied the variations of vorticity distribution, lift and drag coefficients and vortex flow patterns by varying the two parameters. 本論文以計算的方式探討Couette流通過一個往復旋轉的圓柱所形成的流場，進行渦流流洩的控制。圓柱置於中心線上，離兩側板的距離相等。我們設定雷諾數為250（特徵長度為兩側板之間的距離，特徵速度為入流的平均速度）。在計算上，我們使用有限體積法離散統御方程式，並採用隱式法進行時間方向的積分。圓柱後方的流場發展受到兩個參數的影響，分別是圓柱往復旋轉的頻率與旋轉的最高速度；我們變動這些參數，探討渦流強度的分布變化、升力與阻力係數的變化、以及所造成的各種不同流場。結果顯示，在適當的參數組合之下，我們可以有效抑制渦流流洩的發生。