Linking Spatial and Spectral Transport in Two-Dimensional Fluid Flow

****技术摘要****预测非线性非平衡系统的行为仍然是凝聚态物理的巨大挑战。由于它们处于不平衡状态，它们倾向于运动，导致能量和动量在整个系统中流动。但由于它们是非线性的，能量和动量也可以在系统的不同自由度之间重新分配。本项目旨在了解这两种输运在湍流准二维实验室流体流动中的关系，这是一个具有大量强耦合自由度的模型系统。利用被称为过滤空间技术的强大工具，将对空间分辨光谱能量通量进行测量，并随后将其与流中的能量空间输运相关联。这两种输运也将与流场中的自组织相干结构联系起来。该项目将支持一名博士生在实验和将开发的新型计算分析工具方面的培训。***非技术摘要****远离平衡状态并由非线性运动方程控制的物理系统，如流体流动或许多生物系统，在自然界中极为常见。然而，描述和预测它们的行为仍然是一个重大挑战，因为它们倾向于以复杂的方式运动，而且因为扰动倾向于在许多不同的长度和时间尺度上激发反应。通过使用高精度的实验室实验和新颖的分析工具，该项目试图了解空间中的能量流动与不同尺度运动之间的能量流动之间的关系。实验将在近二维湍流中进行，计算分析将用于测量空间和长度尺度之间的能量流动。这些测量结果将有助于更好地理解流动动力学，从而建立大气和海洋中的地球物理流动模型，并揭示流动自组织成连贯结构的机制。博士生将接受非线性物理和流体动力学的培训，获得可转移到许多其他学科的宝贵技能。这项研究的结果将导致对湍流流体流动和更广泛的非线性系统的更深层次的理解，并可能导致表征强耦合凝聚态系统的新方法。

****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.