Collaborative Research: Electrorotational fluid instabilities

粒子可以在电场中自发地开始自转，这一现象被称为Quincke旋转。这个项目将探索电旋转的基本原理和在液滴等流体系统中的应用。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，或者附着在液滴表面的小颗粒可以聚集成漩涡。该项目将实验绘制电旋转流作为流体性质和场强的函数。实验结果将被用来开发模型来解释观察到的不稳定性。除了提高基础知识，这项研究还将为如何利用这些新的电致旋转流动来设计复杂的流动或新的胶体产品，如具有动态表面图案的片状颗粒提供见解。在加州大学圣迭戈分校，PI参与了对当地高中生的工程推广，形式是暑期课程《工程中的流体力学入门：从吸管到飞机》。这项研究的结果可以折叠成材料来支持学生的扩展。泄漏介质液滴的电流体动力流动可能会经历有趣的不稳定性，其中包括旋转流动的产生，例如液滴的稳定倾斜或翻滚，或者像以前在颗粒涂层液滴表面观察到的涡流。这个项目将通过发展(I)基于三维边界积分方法的数值模拟和(Ii)使用渐近方法的分析模型来建立电场中的液滴动力学的这些电致旋转流体不稳定性的机制。将设计和进行实验，以指导和验证计算和分析结果。驱动假设是电致旋转流体不稳定性与Quincke效应(粒子在高于阈值场强的均匀直流电场中自发旋转)有关。研究成果将导致对潜在物理的更深层次的理解，以及发现新的动力机制和工程机会。该提议的潜在变革性在于该系统无法解释的突然出现的行为，可能会启发与复杂流体、不稳定性和界面流动相关的新的研究方向和应用。

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.