Collaborative Research: Electrorotational fluid instabilities

粒子可以自发地在电场中开始旋转，这种现象被称为昆克旋转。本项目将探讨电旋转在流体系统（如液滴）中的基本原理和应用。流体-流体界面可以流动，液滴可以变形，这就产生了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，附着在液滴表面的小颗粒可以聚集成漩涡。该项目将通过实验绘制流体性质和场强的电旋转流函数图。实验结果将用于建立模型来阐明观察到的不稳定性。除了提高基础知识外，该研究还将为如何利用这些新型电旋转流进行复杂流动或新型胶体产品（如具有动态表面图案的斑块颗粒）的工程提供见解。在加州大学圣地亚哥分校，PI一直以暑期课程的形式参与到当地高中生的工程推广中，课程名为“工程流体力学导论：从吸管到飞机”。本研究的结果可以折叠成材料，以支持学生的外展。漏电介质液滴周围的电流体动力学流动可以经历有趣的不稳定性，包括旋转流动的产生，例如液滴稳定倾斜或翻滚，或先前在颗粒涂层液滴表面观察到的漩涡。本项目将通过开发(i)基于三维边界积分法的数值模拟和（ii）使用渐近方法的电场滴动力学分析模型来建立这些电流体不稳定性的机制。将设计并进行实验，以指导和验证计算和分析结果。驱动假说认为，电旋转流体的不稳定性与Quincke效应有关（粒子在均匀直流电场中发生超过阈值场强的自发旋转）。研究成果将导致对潜在物理的更深入的理解，以及发现新的动力机制和工程机会。该提议的潜在变革性质在于，该系统无法解释的紧急行为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.