The influences of “gas” viscosity on water entry of hydrophobic spheres
The influences of “gas” viscosity on water entry of hydrophobic spheres
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DOI：
10.1140/epje/i2019-11795-9
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发表时间：
2019-03
期刊：
影响因子：
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通讯作者：
Feng-Chao Yang;Xiaopeng Chen;P. Yue
中科院分区：
文献类型：
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作者：
Feng-Chao Yang;Xiaopeng Chen;P. Yue
当球体撞击水池时，在球体与自由表面之间发现了一层极薄的气膜。这可能会影响入水空洞的形成和演化。然而，通过正常的数值和实验测试是相当困难的。在这项工作中，通过使用有限元方法，我们研究了水进入的疏水球与气体粘度人为增加。研究了气膜破裂的早期阶段、曲面上的接触线动力学和气穴的形成。数值结果表明，粘性压缩流模型可以很好地定性预测气膜寿命。这与气体膜比球体直径薄得多的事实有关，即使气体粘度是液体粘度的100倍。然而，在液体体积的大部分中可以发现无粘流。自由表面轮廓（或气膜轮廓）则由冲击速度即韦伯数确定。更重要的是，“气体”膜在球体底部破裂后，会产生接触线。接触线沿着球面收缩，收缩速度一般满足规律.这意味着气膜的收缩过程是由惯性-毛细平衡控制的，而不是简单地由粘性-毛细平衡控制的。图形摘要
AbstractAn extremely thin gas film was found between a sphere and a free surface when the sphere impacted onto a water pool. That might influence the generation and evolution of water entry cavity. However, it is quite difficult to be captured through normal numerical and experimental tests. In this work, by using a finite element method we investigate the water entry of a hydrophobic sphere with gas viscosity artificially increased. The air film rupture in the early stage, contact line dynamics on a curved solid surface, and air pocket formation are investigated. The numerical results reveal that the lifetime of the gas film can be predicted by a viscous squeezing flow model qualitatively well. That relates to the fact that the gas film is much thinner than the diameter of the sphere, even when the gas viscosity is 100 times as large as the liquid one. However, inviscid flow can be found in the most part of the liquid bulk. The free surface profile (or the gas film profile) is then determined by the impact speed, namely the Weber number. More importantly, after the “gas” film ruptures at the bottom of the sphere, a contact line is generated. The contact line retracts along the sphere's surface, and the retracting speed fulfilslaw generally. This implies that the retracting process of the gas film is dominated by the inertia-capillary balance, rather than simply by the visco-capillary.Graphical abstract