本研究以自由液滴落下技術搭配液滴切割裝置進行實驗，並觀察兩顆沿流線向液滴碰撞平板的現象分析。探討兩顆液滴群在不同出初始直徑和撞擊表面的傾斜角所造成的效應，並分別觀察四種液滴撞擊狀況: Case 1為單顆液滴撞擊，Case 2為領導液滴欲擴展時尾隨液滴撞擊之，Case 3為領導液滴擴展至最大水平寬度時尾隨液滴撞擊之，Case 4為領導液滴向中心處收縮後欲再次擴展時尾隨液滴撞擊之，其中使用之工作流體為水，液滴撞擊速度控制1.9 ± 0.1 m/s，全部撞擊狀況皆屬低韋伯數撞擊，範圍約40到50。
結果顯示，在垂直撞擊實驗中相同初始液滴直徑下，兩顆液滴撞擊實驗(Cases 2 ~ 4)的最大擴展直徑約為單顆撞擊實驗的1.3倍，並且改變初始液滴直徑來比較930μm與1025μm的差異性，可以觀察到兩者的撞擊特性結果相當類似。在傾斜撞擊實驗中相同初始液滴直徑下，液滴的擴展直徑是降低，在傾斜角0增加到15度。而後傾斜角增加到30度，液滴擴展直徑是上升相較於傾斜角15度。最後傾斜角增加到45度，液滴直擴展直徑又往上升而沒有明顯回縮。在傾斜撞擊實驗中觀察垂直高度的變化，可以發現最大的垂直高度是Cases 3的撞擊實驗不論改變傾斜角皆有相同結果。而隨傾斜角增加，撞擊平板後的穩定液滴的垂直高度隨之下降。

An experimental investigation is performed into the impact characteristics of two streamwise drops impinging on a plate. The drops are generated using a free-falling drop technique and a drop severance device. The experiments are performed using water as the working fluid and a drop velocity of 1.9 ± 0.1 m/s. The experiments have focused particularly on the effects of the initial drop diameter (di) and oblique angle (Φ) of the impinged surface on the impact phenomena. The investigation considers four different impingement conditions differentiated by the different time intervals (Δt), namely Case 1: single drop impingement; Case 2: Δt = Δt1 (the leading drop starting spreading); Case 3: Δt = Δt2 (the leading drop reaching its maximum spreading); and Case 4: Δt =Δt3 (the leading drop reaching its maximum height). Notably, all of the cases correspond to low Weber number impingement (We = 40 ~ 50). It is shown that for the two drop impingement cases (Cases 2 ~ 4), the maximum spreading diameter is around 1.3 times larger than that of the single drop impingement case (Case 1) given the same initial drop diameter and a horizontal flat surface (i.e., Φ = 0°). Moreover, the impact characteristics for an initial drop size of 1025 μm are similar to those for an initial drop size of 930 μm. For a given initial drop diameter, the spreading diameter (dw) decreases as the oblique angle increases from Φ = 0° ~ 15°. However, for Φ = 30°, the spreading diameter increases compared to that for Φ = 15°. As the oblique angle is further increased to 45°, the spreading diameter reaches its maximum value and stabilizes. For a given initial drop diameter, the maximum film height is obtained in the Case 3 impingement condition for all of the considered oblique angles (Φ = 15, 30 and 45°). As the oblique angles increasing, the steady height of the drop decreases.

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