本研究使用數值模擬方法，探討凸出壁面方形噴流，在橫風條件存在與否環境下的流場結構。在無橫風存在環境下，方形管柱射出之噴流為一個穩態而結構固定的放射狀流場結構。在橫風存在環境下，定義噴流對橫風之動量比為R，將流場分為四種模態：下洗模態、橫風支配、過渡模態與噴流支配模態，本研究設定在橫風雷諾數為1000與2074之不同模態下，分析噴流尾流區與管後尾流區的流場衍化與結構。下洗模態，因為垂直噴流動量不足造成管後尾流區強烈的下洗效應；橫風支配模態，因為垂直噴流動量的提升造成管後尾流區之迴流泡抬升至噴流尾流區；過渡模態，剪應層所造成之上剪應力與管後下洗效應的拉扯，造成流體擺盪不定現象產生；噴流支配模態，由於垂直噴流動量遠大於橫風動量，強烈上剪應力造成流體向上流動現象。在三維流場型態方面，馬蹄形渦漩為橫風經過固體柱物最基本的流場結構，於管後尾流區拖曳之流場狀態，了解管後渦漩為主導關鍵；在噴流尾流區下，橫風與噴流交互作用所引致的反向對稱旋轉渦漩對，伴隨周圍流體捲入，擴散效應之範圍愈至下游處，愈有漸增趨勢顯示。藉由數值上的分析，在各模態之噴流最大水平高度、噴流中心傾斜角度方面，動量比為主要影響因素，並藉由數值資料得到剪應力、阻力係數與渦度之定量分析。

This study aims to investigate a jet coming from a square tube in a still environment or in a cross wind using an in-house numerical model. The cross sectional flow structure of a square jet in a still environment is similar to a steady radioactive shape. When the jet interacts with a cross wind, the flow structures can be categorized into four modes according to various momentum ratio of jet to cross flow $R$, i.e. downwash, cross wind dominated, transition, and jet dominated modes. This study reveals evolution of wakes behind the jet and the square tube at Re = 1,000 and 2,074. The downwash mode shows that jet momentum is not strong enough, so the jet is downwashed along the tube. In the cross flow dominated mode, a vortex behind the jet is found.
In the transition mode, the jet begins to swing when traveling downstream.
This phenomenon disappears in the jet dominated mode. The Counter-rotating Vortex Pair (CVP) is clearly shown in the cross sectional structure of the jet in a cross flow. Ambient fluids are entrained into the jet due to CVP.
The numerical results also provide variations of jet height, angle of jet, shear stress and vorticity with respect to varying R.

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