Stability of Partially Wetting Droplet in Wind

PI：Lee，Sungyon Proposal编号：1605947拟议研究的目标是研究在侧风作用下部分湿润表面的水滴的行为。这些曲面并不完美，更像是真实的曲面。日常应用包括窗户上水滴的运动，飞机的除冰，化工过程设备(例如冷凝器中)，喷墨打印，以及环境(雨滴或喷雾水滴在离开表面移动)。水滴附着在表面，然后在风或重力下运行，在自然界中无处不在。液滴脱钉阈值的预测是流体力学中的一个基本问题，也与许多其他工程问题有关。虽然理论存在于低雷诺数区域，但在高雷诺数区域，由于边界层分离的不稳定性，问题变得更加复杂。这一建议的总体目标是通过简化的建模和最先进的实验测量技术，从根本上了解部分润湿液滴在高雷诺数区域的稳定性极限。建议的工作集中在发展一个理论模型，捕捉存在分离边界层流动时的液滴动力学。新开发的液滴模型在时间平均意义上纳入了外部风的影响，以绕过因流动固有的不稳定和液滴表面振荡而产生的困难。初步结果表明，该模型在宏观性质上有效地匹配了单个液滴在粗糙表面上的稳定极限，并扩展到考虑固体突起的影响。同时，还将进一步开发测量仪器，以可视化液滴周围的非稳定空气流动，并改进理论验证所需的接触角测量性能。该项目的更广泛影响包括德克萨斯州高中科学项目的外展活动。液滴问题是一个有吸引力的科学推广问题，因为液滴脱钉既熟悉又难以理解。这个项目将以水滴为例，说明高中数学和物理中引入的抽象概念如何解释物理世界中的现象。PIS将邀请高中科学教师在实验室工作，并根据实验开发课程。这些教师将在他们的课堂上讲授这些内容，并在德克萨斯A&A；M每年举办的教师峰会上报告他们的经历。

PI: Lee, SungyonProposal Number: 1605947The goal of the proposed research is to investigate the behavior of drops that partially wet surfaces under the effect of a cross-wind. The surfaces are imperfect, more like realistic surfaces. Every day applications include the motion of drops on windows, the de-icing of airplanes, chemical process equipment (e.g., in condensers), ink jet printing, and the environment (where rain drops or spray drops move on leave surfaces).Water droplets that adhere to surfaces then run under wind or gravity are ubiquitous in nature. Prediction of droplet depinning thresholds is a problem of fundamental importance in fluid mechanics and is relevant to many other engineering problems. While theories exist in the low Reynolds number regime, the problem becomes more complex in the high-Reynolds-number regime of engineering interest due to the unsteadiness associated with boundary layer separation. The overall objective of this proposal is to gain fundamental understanding of the stability limits of a partially-wetting droplet in the high Reynolds number regime, through reduced modeling and state-of-art experimental measurement techniques. The proposed work focuses on the development of a theoretical model that captures the droplet dynamics in the presence of the separated boundary layer flow. The newly developed droplet model incorporates the effects of the external wind in a time-averaged sense to circumvent the difficulties arising from inherent unsteadiness of the flow and droplet surface oscillations. Preliminary results show that the model effectively matches the stability limits of a single droplet on a rough surface in terms of macroscopic properties and is extended to include the effect of solid protuberance. In parallel, additional development of the measurement instrument will be conducted to visualize the unsteady air flow around the droplet and to improve the performance for contact-angle measurements necessary for theoretical validation. The broader impacts of the project include outreach activities for high school science programs in Texas. The droplet problem is an attractive one for science outreach because droplet depinning is simultaneously familiar yet difficult to understand. This project will use droplets as an example that illustrates how abstractions introduced in high school math and physics can explain phenomena seen in the physical world. The PIs will invite high-school science teachers to work in the lab and to develop curriculum based on the experiment. These teachers will deliver this content to their classes and report on their experiences at a teachers' summit hosted annually at Texas A&M.