Dynamic Observation for Marangoni Flow in a Liquid Bridge of Low-Prandtl Number Liquids

利用热电偶和相移干涉法对半区结构中的Marangoni对流进行了温度振荡和表面振荡的实验研究。对于高雷诺数（Marangoni）区域的不稳定性，各种模式波数出现时间依赖性。即使对于高雷诺数（Marangoni）数条件，只要观察到模式波数的出现频率，也保持液体桥的纵横比和模式波数之间的关系。通过小波变换分析，在Marangoni数为10^4的条件下，观察到了不同频率振荡的能带结构。在低雷诺数（Marangoni）条件下，对部分限制液桥进行了数值模拟，讨论了桥高、开口面积比和开口窗口位置对流动结构和不稳定机制的影响。我们首次发现，两种机制，即，椭圆和离心不稳定性有助于流动模式从静止模式向振荡模式的转变。液桥越短，主流池变得越球形。当打开的窗口位于热区时，情况也是如此。这表明，在这些条件下，椭圆不稳定性变弱，离心不稳定性成为主导。直接转变也被发现时，开放窗口位于热部分的液桥。当开窗口位于冷侧时，流动结构与正常半区结构相似。这种几何结构在实验上有效地减小了Marangoni数。

Temperature oscillation and surface oscillation were examined experimentally using thermocouples and phase-shift interferometry for Marangoni convection in the geometry of a half-zone structure. For instability at high Reynolds (Marangoni) number region, various mode wave numbers appeared time-dependently. The relationship between the aspect ratio of a liquid bridge and mode wave number was kept even for high Reynolds (Marangoni) number conditions, as long as frequency of appearance of mode wave numbers was observed. Trough the wavelet transformation analysis, band structures of oscillations with various frequencies were observed for the condition with the Marangoni number of 10^4. It was also confirmed that the mode wave numbers, which appeared when flow mode transition took place from stationary to oscillator one, were sustained.Under the low Reynolds (Marangoni) number conditions, numerical modeling was performed for the liquid bridge with partial confinement and flow structure and mechanism of instability were discussed as functions of the bridge height, the open area ratio and the position of a open window. We found for the first time that two mechanisms, i.e., elliptical and centrifugal instabilities contribute to flow mode transition from stationary one to oscillatory one. The shorter the liquid bridge is, the more spherical the main flow cell becomes. It is also the case, when the open window is located at the hot are. These suggest that under these conditions elliptical instability becomes weak and that centrifugal instability becomes comparably dominant. Direct transition was also found when the open window is located at the hot portion of the liquid bridge. Flow structure was similar to that of the normal half zone structure, when the open window is located at the cold side. This geometry is effective to reduce the Marangoni number experimentally.