Yun Sungchan
Department of Mechanical Engineering, Korea National University of Transportation, Chungju, 27469, Republic of Korea.
Sci Rep. 2017 Dec 18;7(1):17699. doi: 10.1038/s41598-017-18017-2.
Drop impact on superhydrophobic surfaces has received significant attention because of the advantages of self-cleaning and anti-icing attained by minimum contact time with the surface. Drop hydrodynamics is generally assumed to be axisymmetric, and the contact time is still bounded below by a theoretical Rayleigh limit. In this study, we report an ellipsoidal drop impact on a superhydrophobic surface to demonstrate an efficient way to reduce the contact time and suppress the bounce magnitude by breaking the symmetry. The outcome of the bounce is characterized in terms of a geometric aspect ratio (AR) and Weber number of the drop by comparing the dynamics with a spherical drop. The experimental result shows that the bouncing of the ellipsoidal drop can reduce the contact time and maximum bounce height below the spherical one by at least 30% and 60%, respectively. The exceptional rim dynamics at high AR produces a liquid alignment along the principal direction, leading to the symmetry breaking in the mass and momentum distribution and the subsequent fast drop detachment, which is quantitatively rationalized by the numerical study. The distinct features of the ellipsoidal drop impact will provide an insight into shape-dependent dynamics and open up new opportunities for self-cleaning and anti-icing strategies.
由于与表面的接触时间最短可实现自清洁和防冰等优点，液滴对超疏水表面的撞击受到了广泛关注。通常认为液滴流体动力学是轴对称的，并且接触时间仍受理论瑞利极限的下限限制。在本研究中，我们报告了椭球形液滴对超疏水表面的撞击，以展示一种通过打破对称性来减少接触时间和抑制反弹幅度的有效方法。通过将动力学与球形液滴进行比较，以几何纵横比（AR）和液滴的韦伯数来表征反弹的结果。实验结果表明，椭球形液滴的反弹可使接触时间和最大反弹高度分别比球形液滴至少降低30%和60%。高AR下特殊的边缘动力学产生了沿主方向的液体排列，导致质量和动量分布的对称性破坏以及随后液滴的快速脱离，数值研究对其进行了定量解释。椭球形液滴撞击的独特特征将为形状依赖动力学提供见解，并为自清洁和防冰策略开辟新机会。
