Collaborative Research: Electrorotational fluid instabilities

一个粒子可以在电场中自发地开始旋转，这种现象称为昆克旋转。本计画将探讨电旋转在流体系统如液滴中的基本原理与应用。流体-流体界面可以流动，液滴可以变形，这会产生大量无法解释的流动行为：液滴可以像心脏一样翻滚或跳动，或者附着在液滴表面的小颗粒可以聚集成漩涡。该项目将实验性地绘制电旋转流作为流体性质和场强的函数。实验结果将用于开发模型，以阐明观察到的不稳定性。除了推进基础知识，该研究还将提供有关如何利用这些新型电旋转流进行复杂流或新型胶体产品（如具有动态表面图案的片状颗粒）工程的见解。在加州大学圣地亚哥分校，PI参与了对当地高中学生的工程推广活动，其形式是一个题为“工程中的流体力学入门：从吸管到飞机”的暑期课程。“这项研究的结果可以折叠成材料，以支持学生的推广“关于漏电介质液滴的电流体动力学流动可以经历有趣的不稳定性，其中涉及旋转流动的产生，例如，液滴稳定倾斜或翻滚，或如先前在颗粒涂覆液滴表面上观察到的漩涡。本项目将通过开发（i）基于三维边界积分方法的数值模拟和（ii）使用电场中液滴动力学的渐近方法的分析模型，来确定这些电旋转流体不稳定性的机制。实验将被设计和执行，以指导和验证的计算和分析结果。驱动假设是电旋转流体不稳定性与昆克效应（在阈值场强以上发生的均匀直流电场中粒子的自发旋转）有关。 研究成果将导致对基础物理学的更深入理解，以及发现新的动力学机制和工程机会。该提案的潜在变革性质在于系统的无法解释的紧急行为，这可能会激发与复杂流体，不稳定性和界面流动相关的新研究方向和应用。

A particle can spontaneously start spinning in an electric field, a phenomenon called Quincke rotation. This project will explore fundamentals and applications of electrorotation in fluid systems such as liquid droplets. The fluid-fluid interface can flow and the drop can deform, which creates a plethora of unexplained flow behaviors: a drop can tumble or beat like a heart, or small particles attached to the drop surface can cluster into vortices. The project will experimentally map electrorotational flows as a function of fluid properties and field strength. The experimental results will be used to develop models to elucidate the observed instabilities. In addition to advancing basic knowledge, the research will provide insights on how to harness these novel electrorotational flows for engineering of complex flows or of novel colloidal products such as patchy particles with dynamic surface patterns. At UCSD, the PI has been involved in engineering outreach to local high-school students, in the form of a summer course entitled "Introduction to Fluid Mechanics in Engineering: From a Straw to an Airplane." The results from this research can be folded into materials to support outreach of students"The electrohydrodynamic flow about a leaky-dielectric liquid drop can undergo intriguing instabilities which involve generation of rotational flow, e.g., drop steady tilt or tumbling, or of vortices as previously observed on the surface of particle-coated drops. This project will establish the mechanisms of these electorotational fluid instabilities by developing (i) numerical simulations, based on the three-dimensional Boundary Integral Method, and (ii) analytical models using asymptotic methods, of drop dynamics in electric fields. Experiments will be designed and carried out to guide and validate the computations and analytical results. The driving hypothesis is that electrorotational fluid instabilities are related to the Quincke effect (the spontaneous rotation of a particle in a uniform DC electric field occurring above a threshold field strength). The research outcomes will lead to a much deeper understanding of the underlying physics as well as the discovery of new dynamical regimes and engineering opportunities. The potentially transformative nature of the proposal lies in the unexplained emergent behavior of the system that could inspire new research directions and applications related to complex fluids, instabilities and interfacial flows.