雙液滴碰撞之旋轉分離物理模型研究

Abstract

本研究以同質、等大小雙液滴碰撞為主軸，研究液滴偏心碰撞中旋轉分離區分離機制。觀察過去實驗結果與數值模擬結果，發現在旋轉分離區中存在兩種運動方式，分別是撞擊區在做震盪運動，非撞擊區在做旋轉運動。撞擊區與非撞擊區在關鍵時刻，速度及方向具有良好的匯合，是決定旋轉分離區分離最大的關鍵。以此分離機制來建構旋轉分離區與結合區邊界物理模型。此物理模型與實驗結果有良好的一致性。 我們更進一步分析反射分離區與拉伸分離區之分離機制。以旋轉分離區之物理模型為基準，並針對反射分離區與拉伸分離區之分離機制做出修正後，以同樣的方程式建構出正撞反射分離區與拉伸分離區的邊界物理模型。兩物理模型與實驗結果皆有良好的一致性。 由我們所推導出的物理模型，我們觀察到，正撞反射分離的分離關鍵時間為撞擊區第一次柱狀拉伸時間，旋轉分離的分離關鍵時間為撞擊區第二次柱狀拉伸時間，此結論與前人推測之理論一致：反射分離為撞擊區的拉伸分離，且旋轉分離可稱為二次反射分離。

Identical droplet-droplet collisions were studied, with emphasis on the criterion for boundary transition between regimes of rotational separation and regimes of coalescence. Based on the confirmatory experimental results and the numerical simulation outcomes, two types of motion in the regimes of rotational separation were found to co-exist：region of interaction and the region outside of the region of interaction. The former is oscillating; the latter is rotating. The above two motions achieve good coherence that can overcome the bonding forces at critical time is the fragmentation criterion. A physical model is established and found to agree well with the experimental data. Further analyzing the criterion for reflexive separation and stretching separation, we based the physical model of the rotation separation on head-on reflexive separation and stretching separation. We constructed two new physical models for these two regimes after making some modifications. Both physical models and experimental results are in good agreement. By means of the physical models we established, we observed that the critical time of head-on reflexive separation is the very time while the region of interaction is stretching. On the other hand, the critical time of rotation separation is the second times while the region of interaction is stretching. This outcome is consistent with the previous study that rotational separation is second reflexive separation.