CAREER: Simultaneous Measurement of Wall Deformation and 3-D Flow Structures for Flow-Structure Interaction Investigations

在流动流体和高度灵活的固体边界之间的界面上理解和建模复杂的相互作用是工程和生物学中许多应用的主要挑战。当体流随时间变化或脉动时，这个问题特别难以建模。在心血管疾病和阿尔茨海默氏神经退化的研究中，利用生物表面或柔顺表面进行降噪的流量控制受到了各研究团体的广泛关注。尽管计算方法和理论发展迅速，但可变形表面和近壁流动之间复杂的相互作用仍然只是部分被理解，这阻碍了开发准确模型的努力。详细的实验数据对于指导和验证建模工作是必不可少的。PI的目标是利用最近尖端3d成像技术——数字全息显微镜（DHM）的发展势头，开发一种直接观察和量化界面上复杂相互作用的技术。DHM将同时测量其附近的壁面变形和三维速度场。同时测量是通过记录和跟踪两组粒子来实现的，一组嵌入在变形壁上，另一组位于变形壁上附近的流动中。DHM是唯一能够在3-D中完成这项任务的。随后，该技术将扩展到测量沿变形壁面的压力和应力分布。为了提供样品区域的无障碍视图，测量将在特殊的光学索引匹配设备中进行。这项研究包括仪器的开发，索引匹配的设施和所有接口的方法。该测量技术将应用于研究三种情况下的脉动近壁流动与可变形表面的相互作用：均匀柔顺表面上的脉动流动旨在识别流动结构的异同，刚性和柔顺壁面之间的壁面应力和压力分布；柔度突然变化的表面，旨在研究柔度不均匀性在近壁面流动结构产生中的作用及其对压力和壁面应力分布的影响；以及可变形液滴在柔韧表面上的运动，旨在量化液滴，周围流体和可变形表面之间的相互作用。该阶段将开发具有嵌入颗粒的指数匹配液滴。对近壁相干结构、壁面应力分布、壁面变形条件下的压力等大范围流体特征进行条件采样，可以得到变形引起的流动特性变化。人们还可以通过调节某些流动特性和直接测量表面力来评估流动对壁面变形的贡献。分析将提供水动力载荷与地表变形之间的双向耦合机制。这一测量有望帮助理解这一在工程和生物学中广泛应用的基本主题。它将为社会带来益处，例如通过准确的疾病诊断和患者特定风险评估提供更好的医疗保健。预计这项研究的影响将是广泛的。通过将DHM技术扩展到完全量化三维近壁流动和壁面变形，特别是瞬时压力和壁面应力分布，该技术有可能改变研究领域的格局，并可能带来突破性的发现。研究和教育活动的结合将为一个成功的、全面的学术生涯奠定基础。本科生和研究生将参与研究，这项工作的跨学科性质将反映在PI的教学和建议方法中。目前的教育计划的重点是通过开发一种可以使用现成的手机相机记录数字全息图的工具包来扩大数字全息术的普及。该软件将提供下载，并将在Facebook、MySpace等青少年热门网站上做广告，以吸引大量受众，并招募新的多元化工程专业学生。

CBET-0748149ShengUnderstanding and modeling of complex interactions at the interface between a flowing fluid and a highly flexible solid boundary present major challenges with many applications in engineering and biology. This problem is particularly difficult to model when the bulk flow is time dependent or pulsatile. Flow control using biological surfaces or noise cancellation with compliant surfaces has received considerable attention from various research communities for studying cardiovascular disorders and Alzheimer neurological degeneration. Despite rapid advances in computational methods and theoretical development, complex interactions between deformable surfaces and near-wall flow remain only partially understood, hampering efforts to develop accurate models. Detailed experimental data are essential for guiding and validating modeling efforts. The PI's goal is to harness the momentum gathered during recent development of a cutting-edge 3-D imaging technique, digital holographic microscopy (DHM), to develop a technique to observe and quantify complex interactions at the interface directly. DHM will measure the wall deformation and 3-D velocity field near it simultaneously. The concurrent measurements are achieved by recording and tracking two groups of particles, one embedded in the deforming wall and the other located in the flow near it. DHM is uniquely capable of performing this task in 3-D. Subsequently, the technique will be extended to measure the distributions of pressure and stresses along the deforming wall. To provide unobstructed view on sample area, measurements will be performed in a special optically index-matched facility. This research includes development of instrumentation, an index-matched facility and methodology for all interfaces. This measurement technique will be applied to study three cases of interactions of a pulsating near wall flow with a deformable surface: Pulsating flow over homogeneous compliant surface intended to identify the similarities and differences in flow structure, wall stress and pressure distributions between rigid and compliant walls; a surface with a sudden change in compliance, intended to examine the role of compliance inhomogeneity in the generation of near wall flow structures and their impact on pressure and wall stress distribution; and motion of deformable droplets over a compliant surface, intended to quantify interactions among droplets, surrounding fluids and a deformable surface. Index-matched droplets with embedded particles with be developed for this phase. Conditional sampling over wide range of fluid features such as near wall coherent structure, wall stress distribution, pressure conditioned on wall deformation will obtain deformation-induced changes in flow characteristics. One can also assess the contribution of flow to wall deformation by conditioning upon certain flow characteristics, and from directly measuring surface forces. Analysis will provide two-way coupling mechanism between hydrodynamic loading and surface deformation. This measurement is expected to help understand this fundamental topic with wide range of applications in both engineering and biology. It will provide benefits to society, such as better healthcare through accurate decease diagnosis and patient specific risk assessment. The impacts of the research are expected to be broad. By extending DHM technique to fully quantify 3-D near wall flow and wall deformation, especially instantaneous pressure and wall stress distributions, the technique has a potential of changing the landscape of the research field and may lead to groundbreaking discoveries. The combination of research and educational activities will lay the foundations for a successful, well-rounded academic career. Undergraduate and graduate students will be involved in the research, and the interdisciplinary nature of this work will be reflected in the PI's approach to teaching and advising. The present educational plan is focused on expanding the popularity of digital holography by developing a kit that can record digital holograms using readily available cell-phone cameras. The software will be available for download, and will be advertised through teen popular websites like Facebook, MySpace, to reach a large audience and to recruit new diverse engineering students.