Sliding, pinch-off and detachment of a droplet on a wall in shear flow
Sliding, pinch-off and detachment of a droplet on a wall in shear flow
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DOI：
10.1017/s0022112009992217
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发表时间：
2008-11
影响因子：
3.7
通讯作者：
H. Ding;Mohammad N. H. Gilani;P. Spelt
中科院分区：
文献类型：
--
作者：
H. Ding;Mohammad N. H. Gilani;P. Spelt
我们在这里研究了在施加剪切流的作用下液滴在壁上运动的开始之外发生的情况，考虑了惯性效应和接触角滞后。采用扩散界面法，消除了移动接触线上的剪应力奇异性，得到了有效滑移长度。研究了各种流动形式，包括稳定移动的液滴，部分或整个液滴夹带。在准稳定运动的液滴中，液滴速度在施加的剪切速率中呈线性，但在运动开始时表现出明显的不连续。结果还包括界面与壁面之间的局部最大角度与接触线速度的瞬时值之间的关系。对于固定和移动的液滴，确定了发生夹带的临界条件。发现相应的临界毛细管数在一个相当窄的范围内，即使是相当大的雷诺数值。然后详细研究了断裂的方法，包括在滴上生长的韧带，以及捏颈半径的减小。提出了一个基于能量论证的模型来解释韧带伸长率的结果。本文最后研究了疏水液滴从固体壁上脱离的过程。
We investigate here what happens beyond the onset of motion of a droplet on a wall by the action of an imposed shear flow, accounting for inertial effects and contact-angle hysteresis. A diffuse-interface method is used for this purpose, which alleviates the shear stress singularity at a moving contact line, resulting in an effective slip length. Various flow regimes are investigated, including steadily moving drops, and partial or entire droplet entrainment. In the regime of quasi-steadily moving drops, the drop speed is found to be linear in the imposed shear rate, but to exhibit an apparent discontinuity at the onset of motion. The results also include the relation between a local maximum angle between the interface and the wall and the instantaneous value of the contact-line speed. The critical conditions for the onset of entrainment are determined for pinned as well as for moving drops. The corresponding critical capillary numbers are found to be in a rather narrow range, even for quite substantial values of a Reynolds number. The approach to breakup is then investigated in detail, including the growth of a ligament on a drop, and the reduction of the radius of a pinching neck. A model based on an energy argument is proposed to explain the results for the rate of elongation of ligaments. The paper concludes with an investigation of detachment of a hydrophobic droplet from the solid wall.