6 July 1999 Steady and oscillatory thermocapillary convection generated by a bubble in 1-G and low-G applications
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THree recent microgravity experiments have been hampered by convection caused by unwanted voids and/or bubbles which evolved in the melt. In this paper, we study steady and oscillatory thermocapillary and natural convective flows generated by a bubble in the surrounding fluid environment using a controlled model experiment with silicone oil. The dynamic characteristics of the time-dependent convection are captured using a combined numerical-experimental approach. It is shown that only below the critical Marangoni number, steady states conditions are attainable. With increasing Ma number, there is a complete transition from steady state up to a final non-periodic fluctuating flow regime through several complicated symmetric and asymmetric oscillatory states. The most prevalent oscillatory mode corresponds to a symmetric up and down fluctuation of the temperature and flow fields associated with an axially travelling wave. Careful examination of the numerical results reveals that the origin of this class of convective instability is closely related to an intricate temporal coupling between large-scale thermal structures which develop in the fluid and the temperature sensitive surface of the bubble. Gravity and natural convection play an important role in the formation of these thermal structures and the initiation of the oscillatory convection. Consequently, in low-g, the time evolution of the temperature and flow fields around the bubble are very different from their 1-g counterparts for all Ma numbers.
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Mohammad Kassemi, Mohammad Kassemi, "Steady and oscillatory thermocapillary convection generated by a bubble in 1-G and low-G applications", Proc. SPIE 3792, Materials Research in Low Gravity II, (6 July 1999); doi: 10.1117/12.351273; https://doi.org/10.1117/12.351273

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