非牛顿流体中单气泡运动行为研究

Abstract

利用高速摄像机及数字图像处理技术对单气泡在不同质量分数的羧甲基纤维素钠(CMC)水溶液中的运动行为进行实验测试，得到气泡运动轨迹及上升速度。同时，采用VOF (volume of fluid)模型，模拟计算单气泡在不同质量分数CMC水溶液中的上升过程，考察上升气泡对周围液相场的影响规律。实验结果表明，流变特性对单气泡在CMC水溶液中的运动行为有较大影响。气泡在不同质量分数CMC水溶液中的上升速度沿水深变化规律不同。上升速度的稳定值随CMC水溶液的质量分数增加而减小。摆动运动的强度随CMC水溶液质量分数的增加而减弱，最终气泡趋于直线上升。模拟结果较好再现了单气泡在不同质量分数CMC水溶液中的上升过程。同时还发现，在低质量分数的CMC水溶液中，气泡摆动上升会在尾迹区形成交替漩涡；而在高质量分数的溶液中，尾迹区的液相流场基本按照对称分布。气泡对尾部液相流场的影响范围随着CMC水溶液质量分数的增加而减小。 The high speed photography and digital image processing technique have been employed to measure the rising behavior of the single bubble in carboxymethyl cellulose (CMC) solution to obtain the trajectory and the rising velocity of the bubble. Meanwhile, based on the volume of fluid (VOF) model, numerical simulation has been conducted to study the rising process of the single bubble in CMC solution, and the influence of the rising bubble on the velocity field of the surrounding liquid phase has been investigated. According to the experimental results, the rheological property has great influence on the rising behavior of single bubble in CMC solution. It is shown that the rising velocity of the bubble in the CMC solutions with different weight percentage has different variation patterns. The value of the steady rising velocity decreases with the increase of the weight percentage of the CMC solution. The strength of the oscillation grows weaker with the increase of the weight percentage of CMC solution and eventually tends to ascend along a straight line. The simulation results well predict the bubble’s rising process in CMC solution with different weight percentage. Furthermore, the simulated results show that the bubble generates alternate vortex in CMC solution with lower weight percentage as bubble swings up, while in the CMC solution with higher weight percentage, the flow field of liquid phase distributes symmetrically. The influence domain of the rising bubble on the wake field decreases with the increase of the weight percentage of the CMC solution.