Spatiotemporal Chaos and Particle Dynamics in Complex Flows

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****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.