Surfactant-driven escape from endpinching during contraction of nearly inviscid filaments
Surfactant-driven escape from endpinching during contraction of nearly inviscid filaments
复制标题
在几乎无粘性的细丝收缩过程中，表面活性剂驱动的逃脱末端夹紧
DOI：
10.1017/jfm.2020.476
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发表时间：
2020
影响因子：
3.7
通讯作者：
O. Basaran
中科院分区：
文献类型：
--
作者：
Pritish M. Kamat;Brayden W. Wagoner;A. A. Castrejón;J. Castrejón;Christopher R. Anthony;O. Basaran
摘要在自然界和工业中经常会遇到被气体包围的高度拉伸的液滴或细丝。这种长丝在表面张力的作用下收缩时会表现出复杂和意想不到的动力学。超过临界纵横比的低粘度长丝在其两端经历局部夹断，而不是简单地缩回到相同体积的球体，从而导致一系列子液滴-一种称为端夹断的现象-这是一种原型破碎模式，其不同于在射流破碎中看到的经典瑞利-高原不稳定性。已经表明，在中等粘度的长丝中可以排除端夹，所谓的脱离端夹迄今为止仅定性地理解为由粘性机制引起的。在这里，我们表明，一个类似的逃逸也可以发生在几乎无粘长丝表面活性剂存在于自由表面的反冲长丝。通过数值模拟探讨了逃逸现象的流体动力学。计算结果表明，逃逸是由Marangoni应力驱动的。尽管显然不同的物理起源逃逸在中等粘性的无表面张力的长丝，在几乎无粘性，但表面张力覆盖的长丝，它表明，起源的所有逃逸事件可以归因于一个单一的原因-在弯曲的界面涡的产生。通过分析涡度动力学和涡度的平衡反冲丝，表面张力梯度和伴随的Marangoni应力可以导致逃离endpinching的方式澄清。
Abstract Highly stretched liquid drops, or filaments, surrounded by a gas are routinely encountered in nature and industry. Such filaments can exhibit complex and unexpected dynamics as they contract under the action of surface tension. Instead of simply retracting to a sphere of the same volume, low-viscosity filaments exceeding a critical aspect ratio undergo localized pinch-off at their two ends resulting in a sequence of daughter droplets – a phenomenon called endpinching – which is an archetype breakup mode that is distinct from the classical Rayleigh–Plateau instability seen in jet breakup. It has been shown that endpinching can be precluded in filaments of intermediate viscosity, with the so-called escape from endpinching being understood heretofore only qualitatively as being caused by a viscous mechanism. Here, we show that a similar escape can also occur in nearly inviscid filaments when surfactants are present at the free surface of a recoiling filament. The fluid dynamics of the escape phenomenon is probed by numerical simulations. The computational results are used to show that the escape is driven by the action of Marangoni stress. Despite the apparently distinct physical origins of escape in moderately viscous surfactant-free filaments and that in nearly inviscid but surfactant-covered filaments, it is demonstrated that the genesis of all escape events can be attributed to a single cause – the generation of vorticity at curved interfaces. By analysing vorticity dynamics and the balance of vorticity in recoiling filaments, the manner in which surface tension gradients and concomitant Marangoni stresses can lead to escape from endpinching is clarified.