Division of Physical Sciences and Engineering & Clean Combustion Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands.
Phys Rev E. 2016 Mar;93(3):033128. doi: 10.1103/PhysRevE.93.033128. Epub 2016 Mar 29.
For a limited set of impact conditions, a drop impacting onto a pool can entrap an air bubble as large as its own size. The subsequent rise and rupture of this large bubble plays an important role in aerosol formation and gas transport at the air-sea interface. The large bubble is formed when the impact crater closes up near the pool surface and is known to occur only for drops that are prolate at impact. Herein we use experiments and numerical simulations to show that a concentrated vortex ring, produced in the neck between the drop and the pool, controls the crater deformations and pinchoff. However, it is not the strongest vortex rings that are responsible for the large bubbles, as they interact too strongly with the pool surface and self-destruct. Rather, it is somewhat weaker vortices that can deform the deeper craters, which manage to pinch off the large bubbles. These observations also explain why the strongest and most penetrating vortex rings emerging from drop impacts are not produced by oblate drops but by more prolate drop shapes, as had been observed in previous experiments.
在有限的冲击条件下，液滴冲击水池时可以捕获与其自身大小相当的气泡。随后，大气泡的上升和破裂在气-液界面的气溶胶形成和气体输运中起着重要作用。当撞击坑在靠近水池表面的地方闭合时，大气泡形成，并且已知仅在撞击时为长椭球体的液滴才会发生这种情况。本文通过实验和数值模拟表明，在液滴和水池之间的颈部产生的集中涡环控制着撞击坑的变形和闭合。然而，并非最强的涡环会导致大气泡的产生，因为它们与水池表面的相互作用太强而导致自身破裂。相反，是稍弱一些的涡环能够使更深的撞击坑变形，从而成功地封闭大气泡。这些观察结果还解释了为什么从液滴冲击中产生的最强和最具穿透力的涡环不是由扁球体产生的，而是由先前实验中观察到的更长椭球体形状的液滴产生的。
