Effect of Perturbations on Eddy Organization in Turbulent Boundary Layers

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。最近的研究表明，湍流边界层中大尺度组织的普遍性和重要性被认为是由单个涡旋的包引起的。考虑到包似乎有一个特定的展向间距，PI假设障碍物可以改变展向结构。例如，障碍物可以间隔开，以增强相邻数据包的稳定性，或者干扰并因此改变在光滑壁面上的流动中观察到的典型展向（可能是流向）缩放。在目前的研究中，涡包结构将被扰动的障碍物延伸到边界层的对数区域。本文将分别用体视PIV和层析PIV测量大型水槽装置中边界层的平面速度场和体积速度场。由此产生的速度场将探测与特征识别算法，以确定扰动的影响，涡流和数据包的相互作用，演变和缩放。 将同时量化瞬时剪应力和剪应力梯度，以确定扰动对壁面法向动量传递的潜在影响。 障碍物的高度和展向间距将被改变，以修改数据包的组织。此外，将改变流速以缩放雷诺数的结果，并查看它们如何外推到实际应用中更高雷诺数下的行为。这项研究的结果将有助于回答包的形成是否在边界层中的结果从一个'自下而上'的机制开始附近的墙壁或它的结果从扰动或不稳定性开始远离墙壁。此外，实验将展示如何缩放，组织和伴随的特征可以通过智能控制方法来改变。准确的模型将导致更有效的能源生产和转换过程，更有效的车辆和材料运输，更好地了解污染物，微生物和营养物质在大气和水生环境中的迁移。一名研究生将接受培训，本科生将通过REU补充和UM UROP计划参与研究。此外，PI和学生将与一所拥有大量美国原住民人口的学校的小学教师和学生合作，开发基于火箭，纸飞机和环境流动的互动演示和流动可视化活动。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Longmire0933341 Recent research has demonstrated the prevalence and importance of a large scale organization in turbulent boundary layers thought to be caused by packets of individual eddies. Given that packets appear to have a specific spanwise spacing, the PI hypothesizes that obstacles can alter the spanwise structure. For example, obstacles can be spaced at intervals to either enhance stability of neighboring packets or alternatively interfere with and hence alter the typical spanwise (and probably streamwise) scaling observed in flow over smooth walls. In the current study, the vortex packet structure will be perturbed using obstacles extending into the logarithmic region of the boundary layer. Planar and volumetric velocity fields of boundary layers in a large water channel facility will be measured by stereo and tomographic PIV, respectively. The resulting velocity fields will be probed with feature identification algorithms to determine the effect of perturbations on eddy and packet interaction, evolution, and scaling. Instantaneous shear stresses and shear stress gradients will be quantified simultaneously to determine potential effects of perturbations on wall-normal momentum transfer. Obstacle height and spanwise spacing will be varied to modify the packet organization. Further, the flow speed will be varied to scale the results with Reynolds number and to see how they might extrapolate to behavior at the much higher Reynolds numbers in practical applications. The results of this study will help answer whether packet formation in boundary layers results from a 'bottom up' mechanism initiated near the wall or it results from perturbations or instabilities initiated away from the wall. Further, the experiments will demonstrate how scaling, organization, and accompanying characteristics can be altered by intelligent control methods. Accurate models will lead to more efficient processes in energy production and conversion, more efficient transport of vehicles and materials, better understanding of pollutant, microorganism and nutrient transport in the atmosphere and aquatic environments. One graduate student will be trained, and undergraduate students will participate in the research through REU supplements and the UM UROP program. Also, the PI and students will work with elementary school teachers and students at a school with significant Native American population to develop interactive demonstrations and flow visualization activities based on rockets, paper airplanes, and environmental flows.