Clarification of flow transition of low Prandtl number liquid bridge by ultrasonic visualization

对低普朗特数液桥中的Marangoni对流进行了实验和数值研究。在实验中，首次成功地探测到了轴对称定常流向非对称定常流的转变。此外，还观察到了具有较高驱动力的振荡转变。随着驱动力的增大，振荡流发生分叉，最终出现混沌流。在数值模拟中，建立了模拟实验条件的考虑液桥支撑杆的模型。支撑杆之间的温差逐渐增大，并分析了过渡过程。首先，计算了液桥的直线形状，并在As = 0.8-2.2的宽范围内明确了纵横比（As=高/半径）对过渡条件的影响。此外，振荡热毛细流动的本征正交分解进行了分析。结果，准确地阐明了流动和温度的时空波动。在As=2.0的液桥较长的情况下，讨论了重力和表面变形对临界条件的影响。首次揭示了临界温差和振荡模式随温度梯度方向和与直线形状的偏差而变化。

Experimental and numerical study on Marangoni convection induced in low Prandtl number liquid bridge was carried out. In experiment, the transition from axisymmetrical steady flow to asymmetrical one which was estimated only by numerical simulation succeed to be detected firstly. Furthermore, the oscillatory transition with higher driving force was observed. The oscillatory flow was bifurcated with increasing the driving force of flow and finally chaotic flow was occurred. In numerical simulation, model taken into account of liquid bridge supporting rod which was simulated experimental condition was constructed. Temperature difference between supporting rods was gradually increased and transition process was analyzed. At first, straight shape of liquid bridge was calculated and the effect of aspect ratio (As=high/radius) on the transition condition was made clear across the wide range of As = 0.8-2.2. Moreover the oscillatory thermocapillary flow was analyzed by the proper orthogonal decomposition. As the result, spatio-temporal fluctuation of flow and temperature was precisely clarified. In the case of longer liquid bridge of As=2.0, influence of gravity and surface deformation on critical condition was discussed. It was firstly revealed that the critical temperature difference and oscillatory mode was changed depending on direction of temperature gradient and discrepancy from straight shape.