Linking Spatial and Spectral Transport in Two-Dimensional Fluid Flow

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****Technical Abstract****Predicting the behavior of nonlinear, nonequilibrium systems remains a tremendous challenge for condensed matter physics. Since they are out of equilibrium, they tend to move, leading to a flow of energy and momentum throughout the system. But since they are nonlinear, energy and momentum may also be redistributed among the various degrees of freedom in the system. This project seeks to understand the relationship between these two kinds of transport in a turbulent quasi-two-dimensional laboratory fluid flow, a model system with a very large number of strongly coupled degrees of freedom. Using powerful tools known as filter-space techniques, measurements of the spatially resolved spectral energy fluxes will be made, and will subsequently be correlated with the spatial transport of energy in the flow. These two kinds of transport will also be linked to the self-organized coherent structures in the flow field. The project will support the training of a Ph.D. student in both the experiments and the novel computational analysis tools that will be developed.***Non-Technical Abstract****Physical systems that are far from equilibrium and that are governed by nonlinear equations of motion, such as fluid flows or many biological systems, are extremely common in nature. Characterizing and predicting their behavior, however, remains a significant challenge, both because they tend to move in complicated ways and because perturbations tend to excite responses on many different length and time scales. By using high precision laboratory experiments and novel analysis tools, this project seeks to understand how the flow of energy in space is related to the flow of energy between motions of different scales. Experiments will be conducted in a nearly two-dimensional turbulent fluid flow, and computational analysis will be used to measure the flow of energy both in space and between length scales. These measurements will lead to a better understanding of the flow dynamics, with consequences for models of geophysical flows in the atmosphere and oceans, and will reveal the mechanisms by which the flow self-organizes into coherent structures. A Ph.D. student will be trained in both nonlinear physics and fluid dynamics, gaining valuable skills that are transferable to many other disciplines. The results of this research will lead to a deeper understanding of turbulent fluid flows and to nonlinear systems more broadly, and may lead to new ways of characterize strongly coupled condensed matter systems.