Laboratory Studies of Exact Coherent Structures in Wall Turbulence

0853691 Schatz PI计划对壁湍流的一种新的和根本不同的理论观点进行新颖的实验室测试。光滑壁面附近的有组织流动（相干结构）在雷诺数范围内的湍流产生中起着核心作用。最近的理论工作与大规模的数值计算揭示了一类不稳定的，精确的Navier-Stokes解被称为“精确相干结构”（ECS），它捕捉经典相干结构的基本特征。特别是，理论表明ECS可以用来构造壁湍流的简化描述。虽然理论/数值已经在具有周期性边界条件的高度理想化湍流中提出了基于ECS的描述的令人信服的案例，但对于这种观点是否可以在实验室中描述湍流知之甚少。PI计划在圆形Couette流中进行ECS的实验研究，其中湍流通过精确的光学施加的扰动进行初始化，并通过3D测速仪进行测量。PI独特的光学分布流致动方法已经在其他流中进行了测试;因此，实验将直接关注流动物理而不是致动器的开发。基于ECS的描述的实验室测试将开始首先与适应的理论状态空间可视化技术的实验。然后，实验将识别重要的ECS。特别是，PI将重点关注下分支ECS，它似乎在层流和湍流之间的过渡中发挥关键的"看门人"作用。下分支ECS的特性将为湍流控制的新方法奠定基础。湍流是设计陆地、海上或空中运输车辆时的主要考虑因素。在实际应用中，即使是湍流控制的适度改进也会产生巨大的经济影响。动力系统的工具在解决工程问题中变得越来越重要。因此，我们计划的工作将实施一个实验室模块的状态空间可视化的钟摆动力学，将被列入一个新的介绍性微积分为基础的工程物理课程在格鲁吉亚技术和斯佩尔曼学院，该国领先的历史上黑人学院/大学的妇女。

0853691 SchatzThe PIs plan novel laboratory tests of a new and fundamentally different theoretical view of wall turbulence. Organized flows (coherent structures) near smooth walls play a central role in turbulence production over a wide range of Reynolds numbers. Recent theoretical work with large scale numerical computation has revealed a class of unstable, exact Navier-Stokes solutions termed "exact coherent structures" (ECS), which capture essential features of classic coherent structures. In particular, theory suggests ECS can be used construct simplified descriptions of wall turbulence. While theory/numerics have made a compelling case for an ECS-based description in highly idealized turbulent flows with periodic boundary conditions, very little is known about whether this viewpoint can describe turbulence in the lab. The PIs plan experimental studies of ECS in circular Couette flow where turbulence is initialized by precise, optically-imposed disturbances and measured by 3D velocimetry. The PI's unique method of optical distributed flow actuation has already been tested in other flows; thus, the experiments will focus directly on flow physics instead of actuator development. Laboratory testing of an ECS-based description will begin first with the adaptation of theoretical state space visualization techniques to experiments. The experiments will then identify important ECS. In particular, the PIs will focus on the Lower Branch ECS, which appears to play a key "gatekeeper" role in the transition between laminar and turbulent flow. Characterization of Lower Branch ECS will set the stage for novel approaches to turbulence flow control. Turbulence is a major consideration in the design of transport vehicles on land, at sea or in the air. In practical applications; even modest improvements in turbulence control could have enormous economic impact. The tools of dynamical systems are becoming ever more important in solving engineering problems. Thus, our planned work will implement a laboratory module on state space visualization of pendulum dynamics that will be included in a novel introductory calculus-based engineering physics curriculum at Georgia Tech and at Spelman College, the country's leading Historically Black College/University for women.