Particle-Induced Fingering and Pattern Formation

非技术描述：两种流体（如空气和水）之间的界面动力学表现出各种物理现象。被称为界面不稳定性，流体-流体界面可以变形并产生复杂和规则的图案，例如葡萄酒的眼泪，油漆涂在墙上时的手指，以及液体射流形成的液滴。特别地，当流体相之一包括诸如泥浆（水和砂的混合物）的颗粒时，流体-流体界面的动力学可能甚至更加复杂并且难以预测。除了它们的普遍性之外，控制界面不稳定性在许多工程应用中至关重要，从液滴微流体，纳米颗粒涂层和印刷到制造新的功能材料。虽然这些不同的应用中的许多涉及包含颗粒（也称为悬浮液）的液相，但是悬浮颗粒对界面不稳定性的影响仍然是未知的。因此，理解流体浸没颗粒和流体-流体界面之间的耦合动力学可以影响广泛的应用，甚至导致利用新应用的不稳定性的创新。此外，界面不稳定性构成了一类视觉上令人惊叹的现象，可以很容易地在桌面实验或作为艺术项目的一部分进行演示。因此，研究的视觉方面被纳入一个教育模块和推广活动，将艺术与不同背景和年龄的学生的核心流体力学概念联系起来。这些教育活动旨在让艺术学生参与科学，增加STEM学生的多样性和保留率，并提高公众对基础科学和流体力学的认识和欣赏。技术说明：本提案的总体目标是了解颗粒-液体混合物与气体之间界面不稳定性的物理机制和条件。尽管涉及悬浮液和流体-流体界面的过程无处不在，但流体浸没颗粒对界面不稳定性的影响仍然知之甚少，有机会取得根本性的进展。在该提议中，PI实验性地考虑了两种互补的流动配置，其将气体与非胶体颗粒和粘性液体的混合物界面连接：1）悬浮液置换空气，以及2）空气置换垂直Hele-Shaw池内的悬浮液。与现有技术不同的是，这两种流动配置在没有颗粒的情况下是固有稳定的，使得它们可以隔离悬浮颗粒对流体-流体界面的影响。PI的初步实验已经证明了界面变形和新的颗粒负载结构的出现，这是由颗粒与流体-流体界面的耦合引起的。新的粒子引起的不稳定性的实验测量相结合，减少数学建模和额外的参数研究，发现所需的基本机制，利用不稳定性，并导致新的模式生成的目的。这项基础研究的结果有可能改变目前对悬浮液界面动力学的理解，并使悬浮颗粒的使用能够控制界面不稳定性。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Non-technical Description:The dynamics of interfaces between two fluids, such as air and water, exhibit diverse physical phenomena. Known as interfacial instabilities, fluid-fluid interfaces can deform and generate intricate and regularized patterns, such as tears of wine, fingers of paint as it coats a wall, and droplets forming from a liquid jet. In particular, when one of the fluid phases comprises particles, such as mud (a water and sand mixture), the dynamics of fluid-fluid interfaces can be even more complex and difficult to predict. In addition to their ubiquity, controlling interfacial instabilities is of critical importance in many engineering applications, ranging from droplet microfluidics, nanoparticle coating and printing, to manufacturing new functional materials. While many of these diverse applications involve a liquid phase comprising particles (also known as suspensions), the effects that suspended particles have on the interfacial instabilities are yet unknown. Hence, understanding the coupled dynamics between fluid-immersed particles and fluid-fluid interfaces can impact a wide range of applications and even lead to innovations that harness the instabilities for new applications. In addition, interfacial instabilities constitute a class of visually stunning phenomena that can be easily demonstrated in tabletop experiments or as part of an art project. Hence, the visual aspects of the research are incorporated into an educational module and outreach activities that connect art to core fluid mechanics concepts for students of diverse backgrounds and ages. These educational activities are designed to engage artistic students in science, to increase the diversity and retention of student in STEM, and to enhance awareness and appreciation for fundamental science and fluid mechanics in general public. Technical Description:The overall objective of this proposal is to understand the physical mechanisms and conditions for instabilities on the interface between the particle-liquid mixture and gas. Despite the ubiquity of processes that involve suspensions and fluid-fluid interfaces, the effects of fluid-immersed particles on the interfacial instabilities remain poorly understood, with opportunities for making fundamental advances. In this proposal, the PI experimentally considers two complementary flow configurations that interface gas with the mixture of non-colloidal particles and viscous liquid: 1) the suspension displacing air, and 2) air displacing the suspension inside a vertical Hele-Shaw cell. Distinct from the current state of the art, the two flow configurations are inherently stable without particles, so that they can isolate the effects of suspended particles on the fluid-fluid interface. The PI’s preliminary experiments have demonstrated the emergence of interfacial deformations and new particle-laden structures, which are induced by the coupling of particles with the fluid-fluid interface. Experimental measurements of the novel particle-induced instabilities are combined with reduced mathematical modeling and additional parametric studies, with the aim of discovering the basic mechanisms required to exploit the instability and lead to new pattern generation. The results of this fundamental study have the potential to transform the current understanding of the interfacial dynamics of suspensions and enable the use of suspended particles to control interfacial instabilities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.