本研究針對攻角為零度之二維方柱，於方柱迎風面中央射出一均勻逆向振盪噴流，以振盪噴流對橫風速度比IR (簡稱為注射比)和振盪噴流頻率對尾流渦旋逸放頻率比Rf (簡稱頻率比)為變數，探討橫風雷諾數在1339時，方柱表面流場結構、尾流區渦漩逸放特性以及振盪噴流之動態行為。在一氣動力風洞中，藉由煙霧可視化技術觀察迎風面噴流及方柱尾流之流場特徵。使用熱線風速儀量測方柱尾流區渦漩逸放頻率及其引致之上游流場不穩定性，並分析頻率以及方柱表面流場訊號之相位關係。以PIV技術量化迎風面噴流結構，並與流場可視化之特徵比對。實驗結果顯示，方柱迎風面振盪噴流之特徵模態與注射比IR和頻率比Rf具有密切之關聯性。觀察出兩種流場模態，並命名為尾流主導搖擺模態(wake-dominated flapping jet)和偏折模態 (deflected jet)。在Rf < 1.6與IR< 3 (除了Rf ≈ 1.0時為偏折模態外)以及Rf > 1.6與 0 < IR ≤ 0.8時，主要特徵為尾流主導搖擺模態；在Rf > 1.6與0.8 ≤ IR ≤ 3.0時，流場型態為偏折模態。經流場觀察及訊號分析得知，迎風面停滯點會受到下游渦旋逸放之影響而左右振盪。振盪噴流氣柱噴出時偏折之方向與上游停滯點之瞬間位置有相關性。

The flow characteristics around a square cylinder subject to the influence of an oscillating slot jet injected from the upstream surface of the cylinder was studied by experimental methods. The Reynolds number was 1339. The temporally evolving smoke flow patterns around the square cylinder were revealed by the laser-assisted smoke flow visualization method. The frequency characteristics of the instability waves around the square cylinder were synchronously detected by hot-wire anemometers. The flow field around the upstream cylinder surface was measured by the particle image velocimetry (PIV). Two characteristic flow modes were observed within different ranges of injection ratios (IR) and frequency ratios (Rf), namely the wake-dominated flapping jet and the deflected jet, respectively. At Rf < 1.6 (except for Rf ≈ 1.0) and IR < 3 as well as Rf > 1.6 and 0 < IR ≤ 0.8, the oscillating jet presented a flapping behavior. The flapping motion of the oscillating jet was induced by the oscillating motion of the stagnation point on the upstream surface of the cylinder, which was induced by the vortex shedding in the cylinder wake. The flow pattern in this region was termed the wake-dominated flapping jet. At Rf > 1.6 and 0.8 < IR ≤ 3.0, the injected oscillating slot jet deflected to either the left or the right and attached to the upstream surface. The flow of this mode was named the deflected jet. The deflection direction was dominated by the phase difference between the jet injection timing and the oscillation motion of the vortex shedding in the cylinder wake.

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