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

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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.