振盪參數對液滴撞擊產生氣泡行為與機制的定量研究分析

Abstract

液滴撞擊現象在百餘年來一直是一個被持續研究及探討的領域，直到在Pumphrey & Elmore (1990)提出一液滴撞擊型態地圖後，對整體液滴撞擊深液的各型態才有較系統化的瞭解，雖然世人對各型態分類已經有所認識，但卻仍只僅限部分現象的觀察，例如其並未對會產生氣泡形態的大型漂浮氣泡(Big Floating Bubble)型態做探討以及對水中大氣泡(Large Bubble)型態做深入的探討。此外，液滴在空氣中的振盪行為方面，至今也尚無人探討其對以上液滴撞擊型態的影響。因此在本文當中，將首先以液滴在空氣中自由掉落振盪行為的觀點來觀察其撞擊型態的差異，並且利用數位化的分析方法對其做完整的定量研究且分析。 本文第一部分首先進行高速攝影機拍攝後影像的數位化，藉此分析各撞擊型態的差異。第二部分則對液滴在空氣中自由掉落時的振盪行為進行探討，並利用實驗中的觀察及數位化分析的結果，輔以理論比較來詳細解釋液滴從斷裂產生後開始的振盪模態及如何明顯影響液滴形狀的變化，進而更提出一液滴修正形狀參數(eoffset)，此參數可同時描述兩個模態的變化，且發現此參數對鮮少人探討的大氣泡(Large Bubble)型態有決定性的影響。第三部分則同樣利用數位化分析方式對大型漂浮氣泡(Big Floating Bubble)型態與振盪液滴的關係進行探討。第四部分則利用定量分析結果以及液滴的振盪行為來解釋大氣泡(Large Bubble)型態的氣泡產生機制以及水窪的行為變化，並解說其產生此型態所必要之非常嚴格的初始條件，並將1990年以來被廣為接受的液滴撞擊型態地圖進行修正。

The impact of a droplet on a liquid pool can result in different fantastic phenomena. Many investigations have been conducted since decades; however, none has been studied for the effects of oscillating drop on the large bubble induced by the impacting droplet since Worthington (1908). In the present study, a newest improved quantitative tracking method has been used to analyze the formation and cavity dynamics of big floating bubbles and large bubbles generated by the drop impacting onto deep liquid pool has been experimentally studied and analyzed. Effects of impact velocity, drop size have been investigated and discussed. And it will to understand more deeply about the corresponding relations of those sequential events of drop impact dynamics. Furthermore, two geometry parameter oscillation parameters sharpness-ratio and offset-ratio of the free-falling droplet before impact and Weber number have been found to be the most important controlling parameters. And new characteristic regimes of large bubble area in the V (impact velocity)-d (diameter of droplet) map have been edited. It have been further investigated and analyzed in this thesis.