RUI: Granular Dynamics, and Fluid Mixing in Complex Flows

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This project will investigate nonlinear phenomena exhibited by granular materials and fluids. The project employs small-scale laboratory experiments that are carried out by undergraduate students, who are full partners in the research. There are two main foci for this work: (1) Studies of granular dynamics in sheared and vibrating systems, using sensitive force measurements and rapid particle tracking. This work will reveal how the macroscopic flow properties depend on the internal structure of the material. The role of polydispersity (variations in particle size) will be emphasized, including the suppression of ordering, and segregation induced by shear. Other experiments will explore the statistics of particle motion, slow dynamics and slip in the presence of stress, and novel effects such as collective rotation due to chiral particles lacking reflection symmetry; (2) Methods for highly resolved measurements of stretching in fluid flows will be extended to the important problems of weak turbulence, mixing of non-Newtonian fluids in small devices, and advection in simple chemical reactions. Graduate student and postdoctoral researchers associated with this program learn to mentor undergraduates, and typically assume faculty positions in undergraduate institutions. This project will explore so-called "nonlinear phenomena" exhibited by granular materials and fluids. The project employs small-scale laboratory experiments that are carried out by undergraduate students, who are full partners in the research. There are two main foci for this work: (1) Investigations of sheared and vibrating granular materials will lead to a better understanding of industrial and natural phenomena involving small particles. The experiments will reveal how the macroscopic flow properties depend on the internal structure of the material, and how variations in particle size affect both structure and flow. Other experiments will explore slow creep in the presence of stress, and collective rotation that occurs when particles lack mirror symmetry; (2) Stretching is an important phenomenon in many fluid flows, and methods developed in this program allow its quantitative measurement for the first time. Stretching will be used (a) to characterize and control the mixing of complex fluids such as polymer solutions in small devices that are critical to future technologies, (b) to study weak turbulence, and (c) to investigate the role of flow in chemical reactions. Graduate and postdoctoral researchers associated with this program learn to mentor undergraduates, and typically assume faculty positions in undergraduate institutions.