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

Understanding and modeling of complex interactions occurring at the interface between a flowing fluid and a highly flexible solid boundary, which sometimes involve chemical processes/transport across the interface, are major challenges with many applications in engineering and biology. This problem is particularly difficult to model when the bulk flow is time dependent/pulsatile. Owning to its intimate relationship to our daily life, ranging from human interactions with its surrounding, e.g. flow control using biological surfaces or noise cancellation with compliant surfaces, to high fatality human diseases, e.g. cardiovascular disorders, Alzheimer neurological degeneration, interactions of flow and deformable surface has received considerable attention from various research communities. Despite the rapid advances in computational methods and theoretical development, complex interactions between deformable surfaces and near-wall flow remain only partially understood, hampering the efforts to develop accurate models. Detailed experimental data is essential for guiding and validating modeling efforts. The research goal of this career plan 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/measure complex interactions at the interface directly. We propose to use DHM to 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. The proposed research includes development of instrumentation, (index-matched) facility and methodology for all interfaces. The proposed measurement technique will be applied to study three cases of interactions of a pulsating near wall flow with a deformable surface: (i) 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. (ii) A compliant 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. (iii) 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. Data analysis will use conditional sampling over wide range of fluid features, such as near wall coherent structure, wall stress distribution, pressure conditioned on wall deformation to 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 between hydrodynamic loading and surface deformation.