Laboratory Studies of Exact Coherent Structures in Wall Turbulence

0853691沙茨PI计划对一种新的、完全不同的壁面湍流理论观点进行新的实验室测试。光滑壁面附近的有组织流动(相干结构)在很大范围内的雷诺数范围内对湍流的产生起着核心作用。最近大规模数值计算的理论工作揭示了一类不稳定的、精确的Navier-Stokes解，称为“精确相干结构”(ECS)，它反映了经典相干结构的基本特征。特别是，理论表明ECS可以用来构造壁面湍流的简化描述。虽然理论和数值已经为在具有周期性边界条件的高度理想化的湍流中基于ECS的描述提供了令人信服的理由，但对于这种观点是否能在实验室中描述湍流，我们知之甚少。PI计划对圆形Couette流中的ECS进行实验研究，在圆形Couette流中，湍流由精确的光学施加的扰动初始化，并通过三维测速仪测量。PI独特的光学分布式流动驱动方法已经在其他流动中进行了测试；因此，实验将直接专注于流动物理，而不是执行器的开发。基于ECS的描述的实验室测试将首先从将理论状态空间可视化技术适应实验开始。然后，这些实验将确定重要的ECS。特别是，PI将把重点放在下部分支ECS上，它似乎在层流和湍流之间的过渡中扮演着关键的“把关人”角色。下分支ECS的特性将为湍流控制的新方法奠定基础。在设计陆上、海上或空中运输工具时，湍流是一个主要考虑因素。在实际应用中，即使在湍流控制方面稍有改进，也可能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关于钟摆动力学的状态空间可视化的实验室模块，该模块将包括在佐治亚理工学院和斯佩尔曼学院基于微积分的新型工程物理课程中，斯佩尔曼学院是该国历史上领先的黑人女子学院/大学。

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.