Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India.
Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India.
Phys Rev E. 2018 Apr;97(4-1):043112. doi: 10.1103/PhysRevE.97.043112.
A computational fluid dynamic investigation has been carried out to study the dynamics of a moving compound droplet inside a tube. The motions associated with such a droplet is uncovered by solving the axisymmetric Navier-Stokes equations in which the spatiotemporal evolution of a pair of twin-deformable interfaces has been tracked employing the volume-of-fluid approach. The deformations at the interfaces and their subsequent dynamics are found to be stimulated by the subtle interplay between the capillary and viscous forces. The simulations uncover that when a compound drop composed of concentric inner and outer interfaces migrates inside a tube, initially in the unsteady domain of evolution, the inner drop shifts away from the concentric position to reach a morphology of constant eccentricity at the steady state. The coupled motions of the droplets in the unsteady regime causes a continuous deformation of the inner and outer interfaces to obtain a configuration with a (an) prolate (oblate) shaped outer (inner) interface. The magnitudes of capillary number and viscosity ratio are found to have significant influence on the temporal evolution of the interfacial deformations as well as the eccentricity of the droplets. Further, the simulations uncover that, following the asymmetric deformation of the interfaces, the migrating compound droplet can undergo an uncommon breakup stimulated by a rather irregular pinch-off of the outer shell. The breakup is found to initiate with the thinning of the outer shell followed by the pinch-off. Interestingly, the kinetics of the thinning of outer shell is found to follow two distinct power-law regimes-a swiftly thinning stage at the onset followed by a rate limiting stage before pinch-off, which eventually leads to the uncommon breakup of the migrating compound droplets.
已经进行了计算流体动力学研究，以研究管内移动复合液滴的动力学。通过求解轴对称纳维-斯托克斯方程来揭示与这种液滴相关的运动，其中通过体积法跟踪一对双变形界面的时空演化。界面的变形及其随后的动力学是由毛细力和粘性力之间的微妙相互作用激发的。模拟结果表明，当由同心内外界面组成的复合液滴在管内迁移时，在最初的非稳态演化域中，内液滴从同心位置移动，在稳态时达到恒定偏心率的形态。在非稳态区域中液滴的耦合运动导致内和外界面的连续变形，以获得具有（an）扁长（扁圆）形状的外（内）界面的配置。发现毛细数和粘度比的大小对界面变形的时间演化以及液滴的偏心率有显著影响。此外，模拟结果表明，在界面的不对称变形之后，迁移的复合液滴可能会由于外壳的不规则收缩而经历异常的分裂。分裂是从外壳的变薄开始的，然后是收缩。有趣的是，外壳变薄的动力学被发现遵循两个不同的幂律阶段-起始时迅速变薄阶段，然后是收缩前的速率限制阶段，这最终导致迁移复合液滴的异常分裂。
