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arXiv 1601.06976physics.flu-dyn
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Hele-Shaw池中液滴迁移:润滑膜对液滴动力学的影响

Droplet migration in a Hele-Shaw cell: Effect of the lubrication film on the droplet dynamics

Yue Ling, Jose-Maria Fullana, Stéphane Popinet, Christophe Josserand

摘要:

液滴在Hele-Shaw池中的迁移是一个基本的多相流问题,它对于许多微流体应用至关重要。我们专注于在低毛细管数和三维直接数值模拟进行调查的问题。为了减少计算量,采用自适应网格,仅在界面附近使用高分辨率网格。对液滴水平半径和毛细管数进行了参数研究。对于具有大于通道高度的一半的水平半径的液滴,液滴溢出通道并且呈现出饼形状。液滴与壁面之间形成润滑膜,并特别注意润滑膜对液滴速度的影响。饼状液滴的计算速度被证明是低于平均流入速度,这是与实验测量一致。数值结果表明,润滑膜引起的强烈剪切和三维流动结构都有助于液滴的低流动性。在这种低迁移速度的情况下,液滴参考系中的界面流在顶部朝向后部移动,并且从两个侧边缘反向移动到前部。油滴的速度和润滑膜的厚度随毛细管数的增加而减小。液滴速度及其对毛细管数的依赖性不能被经典的Hele-Shaw方程捕获,因为深度平均近似忽略了润滑膜的影响。

英文摘要:

Droplet migration in a Hele--Shaw cell is a fundamental multiphase flow problem which is crucial for many microfluidics applications. We focus on the regime at low capillary number and three-dimensional direct numerical simulations are performed to investigate the problem. In order to reduce the computational cost, an adaptive mesh is employed and high mesh resolution is only used near the interface. Parametric studies are performed on the droplet horizontal radius and the capillary number. For droplets with an horizontal radius larger than half the channel height the droplet overfills the channel and exhibits a pancake shape. A lubrication film is formed between the droplet and the wall and particular attention is paid to the effect of the lubrication film on the droplet velocity. The computed velocity of the pancake droplet is shown to be lower than the average inflow velocity, which is in agreement with experimental measurements. The numerical results show that both the strong shear induced by the lubrication film and the three-dimensional flow structure contribute to the low mobility of the droplet. In this low-migration-velocity scenario the interfacial flow in the droplet reference frame moves toward the rear on the top and reverses direction moving to the front from the two side edges. The velocity of the pancake droplet and the thickness of the lubrication film are observed to decrease with capillary number. The droplet velocity and its dependence on capillary number cannot be captured by the classic Hele--Shaw equations, since the depth-averaged approximation neglects the effect of the lubrication film.

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