當流體流經縱列雙圓柱障礙物時，由於分離及多重渦流的衍生在雙圓柱間受制與互動，因此較單圓柱周圍流場更為複雜。本文以FLUENT之商用軟體為工具，引用該軟體完整之雷諾應力模式(RSM)以模擬雙圓柱周圍三維紊流發展，以探討縱列雙圓柱流場在不同管間距及不同雷諾數下的流場特性。

　　本文首用流場可視化實驗之數據驗證所建立之模式，進而以該模式模擬不同管徑特徵雷諾數 1000、5000( ， 為漸近流速， 為圓管管徑)上下游兩圓柱圓心不同距離 2、3、4、5( 為兩圓柱圓心連線距)之流場。

　　柱周馬蹄型渦流輪廓、柱後向上流、柱後尾跡渦流在本文數值模擬中，不論是在不同雷諾數或不同管間距下皆可以明顯模擬出來。兩圓柱間流場的主要特性為尾跡流、近液面渦流與底床馬蹄型渦流的交互作用。在不同管間距比的設定下可以觀察到兩圓柱間流場在管間距比2、3與4、5可分為兩個明顯區域，前者不受上游端尾跡流影響，後者受上游端尾跡流影響。另本文使用FLUENT模組對縱列雙圓柱排列的數值模擬研究，對於模式之設定及流場分析之經驗，亦可提供往後使用該模式者在進行數值模擬之參考。

　Because of the interaction of separation and multiple vortices between two circular cylinders, the flow through two aligned circular cylinders is more complex then that of a single one. This study attempts to resolve this complex flow field using the commercial software, FLUENT, since it accommodates the completely module of the Reynolds stress model (RSM) for three-dimensional turbulent flow computation. The distance to diameter ratio of the cylinder, and the Reynolds number based on approach velocity and D are the two main parameters that are concerned in the computations.

　The model constructed is verified by the experimental data from visualization techniques and the model is then used to simulate flows at Reynolds numbers of 1000 and 5000 and various ratios. The horseshoe vortex, up flow and wake flow existed between two circular cylinders can be simulated clearly at those Reynolds numbers and ratios.

　Computed results show that the flows through the aligned circular cylinders are the combinations of the wake flows, the vortex near the water surface and the horseshoe vortex rising from the bottom. The flow features show differently for ratios at 2, 3 and 4, 5. For the flows of the 2 and 3 ratios’, the wake flow generated from the front cylinder interfere with that at the behind, while the distance of the 4, 5 ratios is sufficient that the interferences are lesser than the 2, 3 cases. In addition to these results, the experience gained from the setting up of the computational model using FLUENT can also be a reference for other applications.

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