Stability of Partially Wetting Droplet in Wind

提议的研究目标是调查在侧风作用下部分湿润表面的水滴的行为。表面是不完美的，更像现实的表面。每天的应用包括窗户上的水滴运动，飞机的除冰，化学工艺设备（例如，在冷凝器中），喷墨打印和环境（雨滴或喷雾滴在树叶表面移动）。水滴附着在表面上，然后在风或重力的作用下流动，这在自然界是普遍存在的。液滴脱脱阈值的预测是流体力学中一个非常重要的问题，并且与许多其他工程问题有关。虽然理论存在于低雷诺数区域，但由于边界层分离的不稳定性，在工程感兴趣的高雷诺数区域，问题变得更加复杂。本提案的总体目标是通过简化模型和最先进的实验测量技术，获得对高雷诺数状态下部分润湿液滴稳定性极限的基本理解。提出的工作重点是一个理论模型的发展，捕捉液滴动力学在分离的边界层流动的存在。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，以避免由于流动的固有不稳定性和液滴表面振荡所带来的困难。初步结果表明，该模型在宏观性能上能有效匹配单个液滴在粗糙表面上的稳定性极限，并将其扩展到包含固体凸起的影响。与此同时，测量仪器的进一步发展将被进行，以可视化液滴周围的非稳定气流，并提高理论验证所需的接触角测量的性能。该项目更广泛的影响包括德克萨斯州高中科学课程的推广活动。液滴问题对于科学推广来说是一个有吸引力的问题，因为液滴脱落既熟悉又难以理解。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是如何解释物理世界中看到的现象的。pi将邀请高中科学教师到实验室工作，并根据实验开发课程。这些教师将把这些内容传授给他们的班级，并在每年在德州农工大学举办的教师峰会上报告他们的经验。

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.