中文摘要：

基于COMSOL Multiphysics 4.1层流两相流模型,通过数值模拟研究了连续相流速一定的情况下大接触角（？=160°）的油包水（W/O）液滴绕流微柱阵列的二维运动。通过相场方法考虑表面张力的影响,实现对油-水界面的追踪,获得了W/O液滴的运动状态,重点考查了液滴尺寸对运动特性的影响。模拟结果表明,初始尺寸不同的液滴变形后,长度上存在差异,但厚度基本一致,尺寸介于100？m~150？m液滴的运动速度与液滴尺寸无关。进一步研究了利用尖楔对液滴进行分割的过程,发现液滴脱离末端微柱时,其垂向位置高度与液滴尺寸密切相关,呈先线性增加后趋于定值的特点,利用这一预定位功能及尖楔结构可以获得尺寸可控的均匀子液滴。数值方法与已有实验结果基本一致,且可以很好地表现W/O液滴与微柱的相互作用,揭示液滴的流动细节和运动规律,为设计更为复杂的液滴微流控芯片提供了支撑。

英文摘要：

Based on two-phase flow module in COMSOL Multiphysics 4.1, a numerical simulation about 2-D motion of water in oil（W/O） droplets（contact angle CA=160°） rolling over micro-pillar array is carried out in this paper. Phase field method is adopted to take into account the affect of surface tension and to track the real-time oil-water interface. The effect of droplet size on the movement is emphasized. The simulation results show that W/O droplets will be elongated under the external flow and the lengths of deformed droplets increase with the sizes of droplets, while the widths maintain a constant. It is also reveals that, the velocities of droplets are independent of the sizes（100？m~150？m）of droplets. Furthermore, we consider the droplet splitting with a sharp wedge. When droplet is flushed out from the last micropillar, the vertical locations of droplets relative to last pillar increase linearly firstly and then approaches to a platform. Relying on this pre-position function, the sharp wedge placed at the downstream divides the droplets into two parts. For different sizes of mother droplets, it is found that one of sub-droplet has the same size. Compared to the experimental results, it is believed that the numerical method can be used to simulate the interaction between W/O droplet and micro-pillar very well and reveal the flow details and the motion pattern qualitatively, which is useful to design the complex microfluidic chip in future.