Adebayo Idris T, Matar Omar K
Department of Chemical Engineering, Imperial College London;
Department of Chemical Engineering, Imperial College London.
J Vis Exp. 2018 Aug 18(138):57865. doi: 10.3791/57865.
Droplet impact is a very common phenomenon in nature and attracts attention due to its aesthetic fascination and wide-ranging applications. Previous studies on flowing liquid films have neglected the contributions of spatial structures of waves to the impact outcome, while this has recently been shown to have a significant influence on the drop impact dynamics. In this report, we outline a step-by-step procedure to investigate the effect of periodic inlet forcing of a flowing liquid film leading to the production of spatiotemporally regular wave structures on drop impact dynamics. A function generator in connection with a solenoid valve is used to excite these spatiotemporally regular wave structures on the film surface while the impact dynamics of uniform-sized droplets are captured using a high-speed camera. Three distinct regions are then studied; viz. the capillary wave region preceding the large wave peak, the flat film region, and the wave hump region. The effects of important dimensionless quantities such as film Reynolds, drop Weber and Ohnesorge numbers parameterized by the film flow rate, drop speed, and drop size are also examined. Our results show interesting, hitherto undiscovered dynamics brought about by this application of film inlet forcing of the flowing film for both low and high inertia drops.
液滴冲击是自然界中一种非常常见的现象，因其美学魅力和广泛应用而备受关注。以往关于流动液膜的研究忽略了波的空间结构对冲击结果的影响，而最近的研究表明，这对液滴冲击动力学有显著影响。在本报告中，我们概述了一个逐步的程序，以研究流动液膜的周期性入口强迫对液滴冲击动力学的影响，这种强迫会导致产生时空规则的波结构。一个与电磁阀相连的函数发生器用于激发液膜表面的这些时空规则波结构，同时使用高速摄像机捕捉均匀尺寸液滴的冲击动力学。然后研究了三个不同的区域，即大波峰之前的毛细波区域、平膜区域和波峰区域。还研究了由膜流速、液滴速度和液滴尺寸参数化的重要无量纲量，如膜雷诺数、液滴韦伯数和奥内佐格数的影响。我们的结果显示了有趣的、迄今未被发现的动力学，这是由流动液膜的膜入口强迫对低惯性和高惯性液滴的应用所带来的。
