Experiments on Gravity- and Wind-Driven Droplet Stability and Motion on Rough Surfaces

固体表面上的液滴可以保持固定在表面上，或者由于重力作用而沿着表面向下流动，或者由于外部空气流动而沿着表面流动。液滴在重力作用下的稳定性模型和一些低雷诺数的风力作用下的稳定性模拟已经存在。由于模型验证和接触角变化所需的测量困难，特别是在粗糙表面上，这些模型几乎没有得到实验验证。为了解决这一缺点，一种新的测量技术已经被开发出来，通过跟踪从顶视图图像中穿过液/气界面的激光散斑图案的折射来揭示液滴的界面形状和接触角。该技术将确定接触角如何受到粗糙度振幅和分布的影响。它还将确定现有液滴在重力作用下的静态稳定性模型的准确性，以及它与风力驱动的液滴有何不同。这些问题正在通过测量粗糙金属表面上的蒸馏水滴、倾斜表面上的液滴和倾斜表面上刚好低于临界倾斜角的风力液滴的系统程序来解决。液体从表面润湿和脱落影响着从制造过程到飞机结冰的许多技术领域。除了其广泛的技术影响外，这项工作将为本科生参与研究提供充足的机会。

CBET - 0828469 White, Edward B. Liquid droplets on solid surfaces can remain fixed to the surface, run down the surface due to gravity or run along the surface due to external air flow. Models exist for droplet stability to gravity forcing as do some low-Reynolds-number simulations of stability to wind forcing. These models have received little experimental validation due to the difficulty of measurements needed for model validation and contact angle variation, particularly on rough surfaces. To address this shortcoming, a new measurement technique has been developed that reveals a droplet's interface shape and contact angles by tracking the refraction of a laser speckle pattern across the liquid/gas interface from top-view images. This technique will determine how contact angles are affected by roughness amplitudes and distributions on common engineering metals. It will also determine the accuracy of existing models of droplets' static stability to gravity forcing and how it differs from wind-driven droplets. These questions are being addressed through a systematic program of measurements of distilled-water droplets on rough metal surfaces, droplets on inclined surfaces and measurements of wind-driven droplets on inclined surfaces just below critical inclination angles. Wetting and shedding of liquids from surfaces affect numerous areas of technology from manufacturing processes to aircraft icing. Beyond its broad technological impacts, the work will provide ample opportunities for undergraduate research participation.