Elucidating the Flow Structure and Addressing Modeling Issues in Turbulent Boundary Layers Based on Multiscale, 3D Velocity Measurements

基于多尺度 3D 速度测量阐明湍流边界层中的流动结构并解决建模问题

• 批准号: 0932941
• 负责人: Joseph Katz
• 金额: $ 40万
• 依托单位: Johns Hopkins University
• 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: 2009-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0932941&HistoricalAwards=false
• 关键词: Elucidating; Flow; Structure; Addressing; Modeling

Katz0932941High Reynolds number turbulent boundary layers continue to pose major scientific and technological challenges due to their inherently complex couplings of dynamics across many length and time scales. Integration of recently introduced techniques enables 3D high-resolution volumetric velocity measurements across a range of scales, from very near the wall to the outer part of the boundary layer. The objective of this study is to experimentally investigate interactions among buffer layer vortices and outer (inertial) layer, larger-scale structures above a smooth wall at moderate to high Reynolds numbers. Data analysis will examine effects of mean flow acceleration and local instantaneous pressure gradients on the characteristics of buffer layer vortices and their effects on turbulence statistics. The study will also address fundamental Large-Eddy Simulation (LES) issues in wall-bounded flows, especially modeling of wall shear stresses in terms of large-scale features that are resolved in LES, and impact of unsteadiness, local pressure gradient, and instantaneous streamwise curvature on the wall stress. Finally, the PIs will develop a systematic method for determining the length-scale required for fully resolving the inner boundary layer flow, both experimentally and numerically. The multi-scale velocity measurements will be performed by simultaneously implementing two state-of-the-art, 3D flow measurement techniques: Relatively "coarse" measurements will be performed using tomographic particle image velocimetry (PIV) at a spatial resolution of 0.5mm. High-resolution velocity measurements near the wall within part of the coarse volume will be performed using digital holographic microscopy (DHM), at a spatial resolution of 20 um. Also, using recently introduced procedures, four-exposure DHM will measure the instantaneous distribution of material acceleration, and provide the local pressure gradients. Experiments will be performed in the optically index-matched facility at JHU that enables unobstructed near-wall measurements, even near rough walls and curved boundaries used for generating mean pressure gradients. In-line DHM, a high-resolution flow measurement technique recently developed in the PIs' laboratory, involves acquisition of in-line holograms of a seeded flow by a digital camera. Numerical reconstruction and particle tracking provide the 3D velocity distribution. The present optical setup and data analysis procedures will be further developed for simultaneous application with tomographic PIV. DHM extends the depth of field of a conventional microscope by 3 orders of magnitude, and may revolutionize microscopy in many other fields that require measurements of 3D dynamic processes as in swimming of bacterial suspensions. The PIs have been active in disseminating holographic microscopy by providing software, training and follow-up assistance to personnel in several academic laboratories, including Rutgers, LSU and VA Tech. The PIs will continue their long-term commitment to and record of success at involving undergraduate students in laboratory and field research, as part of the PIs' effort to motivate them to pursue graduate education. The PIs will also continue engaging high school students from Baltimore Polytechnic in an extensive, yearlong research experience as part of their Research Practicum.

Katz0932941高雷诺数湍流边界层由于其在许多长度和时间尺度上固有的复杂动力学耦合而继续构成重大科学和技术挑战。集成最近推出的技术可以在一系列尺度上进行 3D 高分辨率体积速度测量，从非常靠近壁的地方到边界层的外部。本研究的目的是通过实验研究缓冲层涡流与外（惯性）层、光滑壁上方的中等到高雷诺数的较大规模结构之间的相互作用。数据分析将检查平均流动加速度和局部瞬时压力梯度对缓冲层涡流特征的影响及其对湍流统计的影响。该研究还将解决壁面边界流中的基本大涡模拟 (LES) 问题，特别是根据 LES 中解决的大尺度特征对壁面剪应力进行建模，以及不稳定性、局部压力梯度和瞬时流向曲率对壁面应力的影响。最后，PI 将开发一种系统方法，用于通过实验和数值确定完全解析内边界层流动所需的长度尺度。多尺度速度测量将通过同时实施两种最先进的 3D 流量测量技术来进行：相对“粗略”的测量将使用断层扫描粒子图像测速 (PIV) 以 0.5 毫米的空间分辨率进行。将使用数字全息显微镜 (DHM) 以 20 微米的空间分辨率对部分粗体积内的壁附近进行高分辨率速度测量。此外，使用最近推出的程序，四次曝光 DHM 将测量材料加速度的瞬时分布，并提供局部压力梯度。实验将在约翰霍普金斯大学的光学折射率匹配设施中进行，该设施可以无障碍地进行近壁测量，甚至可以在粗糙的墙壁和用于生成平均压力梯度的弯曲边界附近进行测量。在线 DHM 是 PI 实验室最近开发的一种高分辨率流量测量技术，涉及通过数码相机采集种子流的在线全息图。数值重建和粒子跟踪提供了 3D 速度分布。目前的光学设置和数据分析程序将进一步开发，以便与断层成像 PIV 同时应用。 DHM 将传统显微镜的景深扩展了 3 个数量级，并且可能会在许多其他需要测量 3D 动态过程（例如细菌悬浮液游动）的领域中彻底改变显微镜技术。 PI 一直积极传播全息显微镜，为罗格斯大学、路易斯安那州立大学和 VA Tech 等多个学术实验室的人员提供软件、培训和后续援助。作为 PI 激励本科生接受研究生教育的努力的一部分，PI 将继续长期致力于让本科生参与实验室和实地研究并取得成功。作为研究实习的一部分，PI 还将继续让巴尔的摩理工学院的高中生参与为期一年的广泛研究经验。