Abstract The spontaneous bubble migration and the active manipulation have widely applications in outer space. In this paper, the bubble migration driven by the thermal capillary effect is numerically investigated under variable buoyancy. The numerical model is built up through the transient two-dimensional axisymmetric model with a level set method. It is found that the magnitude and direction of bubble migration velocity is determined by the competition of upward buoyant effect and downward thermal capillary effect. These two effects can be controlled by changing the ratios of density, viscosity, thermal conductivity of bubble over surrounding liquid, as well as Reynolds number, Froude number, Peclet number and Marangoni number. With increasing Froude number or decreasing density ratio, the thermal capillary effect becomes dominant over the buoyant effect, the bubble will migrate from upward to downward. The Marangoni number has negligible effect on the bubble migration at low Reynolds numbers, while at high Reynolds numbers, increasing Marangoni number can reduce the upward migration velocity due to stronger thermal capillary effect. At low Reynolds numbers, with the increasing ratios of viscosity and thermal conductivity, the downward driving force is increased, while at high Reynolds numbers, the ratios have negligible effect on the bubble migration. These findings may provide the guidance for actively manipulating the bubbles under variable buoyancy.

中文翻译：

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可变浮力下通过热毛细管效应操纵气泡迁移

摘要 气泡自发迁移和主动操纵在外太空有着广泛的应用。本文对可变浮力下由热毛细管效应驱动的气泡迁移进行了数值研究。数值模型是通过瞬态二维轴对称模型用水平集方法建立的。发现气泡迁移速度的大小和方向是由向上的浮力效应和向下的热毛细管效应的竞争决定的。这两种效应可以通过改变密度、粘度、气泡与周围液体的热导率以及雷诺数、弗劳德数、佩克莱特数和马兰戈尼数的比率来控制。随着弗劳德数的增加或密度比的降低，热毛细管效应比浮力效应占主导地位，气泡将从上向下迁移。Marangoni 数在低雷诺数下对气泡迁移的影响可以忽略不计，而在高雷诺数下，由于更强的热毛细管效应，增加 Marangoni 数可以降低向上迁移速度。在低雷诺数下，随着粘度和热导率比率的增加，向下的驱动力增加，而在高雷诺数下，比率对气泡迁移的影响可以忽略不计。这些发现可能为在可变浮力下主动操纵气泡提供指导。而在高雷诺数下，由于更强的热毛细管效应，增加马兰戈尼数可以降低向上迁移速度。在低雷诺数下，随着粘度和热导率比率的增加，向下的驱动力增加，而在高雷诺数下，比率对气泡迁移的影响可以忽略不计。这些发现可能为在可变浮力下主动操纵气泡提供指导。而在高雷诺数下，由于更强的热毛细管效应，增加马兰戈尼数可以降低向上迁移速度。在低雷诺数下，随着粘度和热导率比率的增加，向下的驱动力增加，而在高雷诺数下，比率对气泡迁移的影响可以忽略不计。这些发现可能为在可变浮力下主动操纵气泡提供指导。