Two Problems in Viscous Flow: Fluid-Structure Interaction and Contact Drop Formation

Qian, Bian

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Year:: 2010
Contributor:: Qian, Bian (creator); Breuer, Kenneth (Director); Powers, Thomas (Reader); Maxey, Martin (Reader); Tripathi, Anubhav (Reader); Brown University. ENGINEERING: Fluids, Thermal, and Chemical Processing (sponsor)
Genre:: theses
Subject:: hydrodynamic synchronization; contact drop formation; liquid bridge; Fluid-structure interaction
Extent:: xv, 102 p.
DOI: https://doi.org/10.7301/Z0028PSC

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Description

Abstract:: This thesis deals with two problems in viscous flow.In the first part, fluid-structure interactions were investigated, with connections to swimming microorganisms. Motivated by a numerically proposed swimming mechanism, we studied an elastic straight rod rotating on an imaginary cone. The shapes of the rod which rotates at either prescribed torques or speeds were experimentally measured and theoretically calculated. The rod undergoes a discontinuous transition to a helical shape at a critical torque, with increased propulsion force. A simple model was presented to capture and explain the essential physics. In addition, the longstanding hypothesis of hydrodynamic synchronization was investigated using a scale model experiment. We demonstrated that hydrodynamic interactions can cause synchronization between rotating paddles driven at constant torque if the shafts supporting the paddles have some flexibility. The synchronization state depends on the symmetry of the paddles and the torque mismatch. Excellent agreements were shown between the experiments and the regularized stokeslets simulations. And a simple analytic theory was built to predict the synchronization time as a function of paddle separation.In the second part, contact drop formation on a hydrophobic surface was examined experimentally and theoretically. A wide range of droplet sizes can result from the same syringe by varying the dispensing speed. Three dispensing regimes were identified according to the motion of the contact line, a line coexisting between liquid/vapor/solid interfaces. In the fixed and the expanding contact-line regimes, a power dependence of the drop sizes on the dispensing speeds was observed experimentally and obtained theoretically. In the receding contact-line regime, the contact-line motion consists of two stages: a slow retraction at the beginning and a rapid retraction immediately prior to drop breakup. The dispensing process was modeled as a stretching liquid bridge with a free moving contact-line. A quasi-static analysis and numerical calculations were performed to accurately predict the initial evolution of the liquid bridge and the final breakup respectively. The influences of the contact-line movement on the onset instabilities of liquid bridges and thus the deposited drop sizes were discussed.
Notes:: Thesis (Ph.D. -- Brown University (2010)

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Rights: In Copyright
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Citation

Qian, Bian, "Two Problems in Viscous Flow: Fluid-Structure Interaction and Contact Drop Formation" (2010). Fluid, Thermal, and Chemical Processes Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0028PSC

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Fluid, Thermal, and Chemical Processes Theses and Dissertations

Theses and Dissertations for the Fluid, Thermal, and Chemical Processes department.
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