We numerically study the head-on collisions of two immiscible droplets of different components and focus on the effects of droplet inertia and interfaces, which are expected to play a crucial role in the interaction between the two droplets. A ternary-fluid diffuse-interface method is used here after being validated by comparing against experiments of the collision between an aqueous droplet and a silicone oil droplet. In order to figure out how the droplet inertia and interfaces affect the dynamic behavior after the collision, axisymmetric simulations are performed with various Weber number We and surface tension ratio λ, i.e., the ratio of the surface tension coefficient of the liquid–liquid to the liquid–gas interfaces. Their effects on the film thickness, maximal deformation of the colliding droplets, and the corresponding contact time are investigated. To describe the collision dynamics, we propose an equivalent surface tension σ^* based on the analysis of the energy conservation and morphology of the colliding droplets. Using the equivalent surface tension σ^*, we theoretically predict the film thickness, maximal spreading time, and deformation of the colliding droplets. The theoretical predictions are in good agreement with the numerical results.

中文翻译：

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不同成分的两个不混溶液滴的正面碰撞

我们数值研究了两个不同成分的不混溶液滴的正面碰撞，并着重研究了液滴惯性和界面的作用，这些作用在两个液滴之间的相互作用中起着至关重要的作用。通过与水液滴和硅油液滴之间的碰撞实验进行对比验证，此处使用了三元流体扩散界面方法。为了找出碰撞后液滴的惯性和界面如何影响动力学行为，使用各种韦伯数We和表面张力比λ进行轴对称仿真即液-液界面与液-气界面的表面张力系数之比。研究了它们对薄膜厚度，碰撞液滴最大变形以及相应的接触时间的影响。为了描述碰撞动力学，我们基于碰撞液滴的能量守恒和形态分析提出了等效表面张力σ ^*。使用等效表面张力σ ^*，我们从理论上预测膜厚度，最大扩展时间和碰撞液滴的变形。理论预测与数值结果吻合良好。