Droplet-wall interactions are well known to generate a wide variety of outcomes such as spreading, splashing, receding, jetting, and rebounding. In this paper, we focus on the evolution of jets that form during the recoil of impinging drops on partially wetting hydrophilic substrates composed of cylindrical micropillars. The impact of the millimeter-sized drops of water-glycerol mixtures on the microstructured hydrophilic substrates is investigated by high-speed video photography. Impact velocity and fluid viscosity are varied to characterize the jets. Wetting angles are maintained in the range of $43.6^{\circ }\le \theta \le 51.4^{\circ }$. A regime map is constructed to convey the jet behavior at a glance. We find that jet speed, height, and diameter scale linearly with the Weber number. We also find that the jet originates from the inertial collapse of an air cavity formed during the recoil phase of the drop following impact on the microstructured substrate. The relationship between the size of the top jet drop and jet velocity obeys the scaling law of [Gañán-Calvo, Phys. Rev. Lett. 119, 204502 (2017)] for jets induced by capillary surface singularities. No jet is observed for sufficiently high drop viscosity.

中文翻译：

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液滴撞击微柱状亲水性基材后的喷射流

众所周知，液滴与壁的相互作用会产生各种各样的结果，例如散布，飞溅，后退，喷射和回弹。在本文中，我们专注于在由圆柱形微柱组成的部分润湿的亲水性基材上撞击液滴的反冲过程中形成的射流的演变。通过高速视频摄影研究了毫米大小的水甘油混合物液滴对微结构亲水性基材的影响。改变冲击速度和流体粘度以表征射流。润湿角保持在$43。6^{\circ }\le \theta \le 51。4^{\circ }$。构造状态图以一目了然地传达喷射行为。我们发现射流速度，高度和直径与韦伯数成线性比例关系。我们还发现，射流起源于液滴的反冲阶段期间形成的气穴的惯性坍塌，该气穴在撞击微结构化基底之后形成。顶部射流的大小与射流速度之间的关系遵循[Gañán-Calvo，Phys。牧师 119，204502（2017）]用于通过毛细管表面奇点诱导的射流。没有观察到足够高的液滴粘度的喷射。