單一渦穴氣泡產生與氣泡破裂流場之量測研究

Generation of Single Cavitation Bubble and Measurements of Bubble Collapse Flow

為探討渦穴氣泡破裂於固體邊界附近所產生之流場特性與氣泡破裂過程中之形成逆向噴流的原因，本研究以旋轉U型平台設備於轉軸中心位置產生單一渦穴氣泡，並藉由高速攝影機拍攝之影像以分析氣泡破裂流場特性。實驗中發現，氣泡受到液體噴流之壓縮後突破氣泡表面可產生Kelvin-Helmholtz渦流。當氣泡中心距離固體邊界的位置介於1至3倍氣泡半徑之間時，液體噴流突破氣泡表面後至撞擊固體界面，是否產生滯流環為逆向噴流形成之關鍵因素。利用較低的壓力波強度擊破氣泡，可延長氣泡破裂時間之特性，可清楚呈現氣泡破裂的流場特性與及逆向噴流之成因，各種複雜的渦穴氣泡破裂流場特性，均清楚呈現於本研究中。

This research aims to investigate the flow field characteristics of the collapse process of a single cavitation bubble and the cause of the counter jet resulted from this process. In this study, a U-tube platform was set up in rotation mode for the generation of single cavitation bubbles at the center of the rotating axis while a high speed camera was arranged to record the flow field. It was found that a Kelvin-Helmholtz vortex was formed when a bubble was compressed and deformed and a liquid jet penetrated the bubble surface. If the distance between the bubble center and the solid boundary is within one to three times of the bubble’s radius, a stagnation ring will form on the boundary, a key to the formation of the counter jet when the bubble is impinged by the liquid jet. Using a low strength pressure wave for the compression of the cavitation bubble could extend the bubble collapse time and therefore lead to a better understanding of the flow field features and of the counter jet features in the process of bubble collapse. The complex phenomenon of cavitation bubble collapse flows was clearly manifested in this study.