Experimental study on the transition process to the oscillatory thermocapillary convections in a floating half zone |
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Authors: | Y Aa Z H Cao Z M Tang Z W Sun W R Hu |
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Affiliation: | (1) National Microgravity Laboratory, CAS, Institute of Mechanics, Chinese Academy of Sciences, No. 15 Beisihuanxi Road, 100080 Beijing, China |
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Abstract: | The transition process of the thermocapillary convection from a steady and axisymmetric mode to the oscillatory mode in a
liquid bridge with a fixed aspect ratio and varied volume ratio was studied experimentally. To ensure the surface tension
to play an important role in the ground-based experiment, the geometrical configuration of the liquid bridge was so designed
that the associated dynamic Bond number Bd≈1. The velocity fields were measured by Particle Image Velocimetry (PIV) technique to effectively distinguish the different
flow modes during the transition period in the experiments. Our experiments showed that as the temperature difference increased
the slender and fat bridges presented quite different features on the evolution in their flow feature: for the former the
thermocapillary convection transformed from a steady and axisymmetric pattern directly into an oscillatory one; but for the
latter a transition flow status, characterized by an axial asymmetric steady convection, appeared before reaching the oscillatory
mode. Experimental observations agree with the results of numerical simulations and it is obvious that the volume of liquid
bridge is a sensitive geometric parameter. In addition, at the initial stage of the oscillation, for the former a rotating
oscillatory convection with azimuthal wave number m=1 was observed while for the latter a pulsating oscillatory pattern with
azimuthal wave number m=2 emerged, and then with further increase of the temperature difference, the pulsating oscillatory
convection with azimuthal wave number m=2 evolved into a rotating oscillatory pattern with azimuthal wave number m=2. |
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