Laboratory Studies of Exact Coherent Structures in Wall Turbulence

壁湍流中精确相干结构的实验室研究

• 批准号: 0853691
• 负责人: Michael Schatz
• 金额: $ 30万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0853691&HistoricalAwards=false
• 关键词: Laboratory; Studies; Exact; Coherent; Structures

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.

0853691 Schatz PI 计划对一种全新的、根本不同的壁湍流理论观点进行新颖的实验室测试。光滑壁附近的有组织的流动（相干结构）在大范围雷诺数的湍流产生中发挥着核心作用。最近的大规模数值计算理论工作揭示了一类不稳定的精确纳维-斯托克斯解，称为“精确相干结构”（ECS），它捕获了经典相干结构的基本特征。特别是，理论表明 ECS 可用于构建壁湍流的简化描述。虽然理论/数值已经为具有周期性边界条件的高度理想化湍流中基于 ECS 的描述提供了令人信服的案例，但人们对这种观点是否可以描述实验室中的湍流知之甚少。 PI 计划对圆形库埃特流中的 ECS 进行实验研究，其中湍流通过精确的光学施加扰动来初始化，并通过 3D 测速仪进行测量。 PI独特的光分布式流驱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学而不是执行器开发。基于 ECS 的描述的实验室测试将首先从理论状态空间可视化技术适应实验开始。然后实验将确定重要的 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着关键的“看门人”作用。下分支 ECS 的表征将为湍流控制的新方法奠定基础。湍流是陆地、海上或空中运输车辆设计的主要考虑因素。在实际应用中；即使湍流控制方面的微小改进也可能产生巨大的经济影响。动力系统工具在解决工程问题方面变得越来越重要。因此，我们计划的工作将实施一个关于摆动力学状态空间可视化的实验室模块，该模块将包含在佐治亚理工学院和斯佩尔曼学院（该国领先的历史黑人女子学院/大学）基于微积分的新颖工程物理入门课程中。