Spatiotemporal Chaos and Particle Dynamics in Complex Flows

*非技术摘要*研究流体流动的公认方法依赖于跟踪悬浮粒子，悬浮粒子被假定跟随流体的运动。然而，在某些情况下，这一假设可能会失败，让人对这种测量的可靠性产生怀疑。因此，更好地了解流体中颗粒的运动是很重要的。该项目在一个以本科生为主的机构进行，将专注于粒子惯性在造成理想粒子运动偏差方面的作用，并可能提供一种改进流体动力学测量方法的方法。在相关工作中，该项目将使用跟踪的粒子来研究从规则流体流动到混沌流动状态的转变，在这种状态下，流动变得不可预测。这种流动很普遍，考验着我们对复杂状态的理解。该项目将采用的新方法包括通过定位流动模式的独特特征来表征复杂的流动模式，例如局部旋转中心或漩涡。实验将通过将一名博士后实习生与本科生配对进行。这种方法为双方提供了重要的培训优势。颗粒在流体中的运动不仅是材料科学的一个基本课题，而且为研究流体流动提供了一种强大的诊断方法，因此具有重要意义。这个项目在一个以本科生为主的机构，将通过小规模的良好控制的实验室实验来探索流体中颗粒动力学的主题。研究了中等雷诺数时不同大小颗粒在流动中的运动，以了解颗粒如何？随着惯性的增加，他们的行为也会发生变化。一个重要的结果将是了解输送的颗粒在什么条件下可以用作被动流动示踪剂，这是几乎每一种现代流动测量技术所假定的。将研究浮动剪切颗粒层的行为，以深入了解软材料的变形，而在微通道中流动的颗粒将能够研究向不可逆流的转变。最后，该项目将通过确定粒子轨迹的曲率来研究向时空混沌的转变。这种新的方法可以确定复杂流体流动的特殊拓扑特征，并随着流动从规则流动到时空混沌状态的转变而随时间进行跟踪。在本研究中，博士后实习生和本科生的配对为双方提供了重要的培训优势。

****NON-TECHNICAL ABSTRACT****The accepted methods of studying fluid flows rely on tracking suspended particles, which are assumed to follow the motion of the fluid. However, in some cases this assumption may fail, casting doubt on the reliability of such measurements. Hence, it is important to achieve a better understanding of the motion of particles in fluid flows. The project, at a predominately undergraduate institution, will focus on the role of the inertia of particles in causing deviations from ideal particle motion, and potentially provides a way to improve fluid dynamical measurement methods. In related work, the project will use tracked particles to investigate the transition from regular fluid flow to the state of chaotic flow, where the flow becomes unpredictable. Such flows are widespread, and test our understanding of complex states. The novel method to be employed in the project involves the characterization of complex flow patterns by locating unique features of the flow pattern, such as the centers of local rotation, or vortices. The experiments will be conducted by pairing a postdoctoral trainee with undergraduate students. This approach provides important training advantages for both. ****TECHNICAL ABSTRACT****The motion of particles in fluids is important both as a fundamental topic in materials science, and because it provides a powerful diagnostic method of studying fluid flow. This project at a predominately undergraduate institution, will explore the theme of particle dynamics in fluids by means of small-scale well-controlled laboratory experiments. The motion of particles of varying sizes in flows at modest Reynolds number is investigated, to understand how the particles? behavior changes as their inertia increases. An important result will be to understand the conditions under which transported particles can serve as passive flow tracers, as is assumed for nearly every modern flow measurement technique. The behavior of a floating sheared layer of particles will be studied to gain insight into the deformation of soft materials, and particles flowing in a micro-channel will allow study of the transition to irreversible flow. Finally, the project will investigate the transition to space-time chaos by determining the curvature of particle trajectories. This novel method allows the special topological features of a complex fluid flow to be determined, and to be tracked over time as the flow makes a transition from regular flow to the state of space-time chaos. The pairing of a postdoctoral trainee with undergraduate students in this research provides important training advantages for both.