Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session PU: Viscous Flows II |
Hide Abstracts |
Chair: Nivedita Gupta, University of New Hampshire Room: 200I |
Tuesday, November 24, 2009 11:40AM - 11:53AM |
PU.00001: Colloidal crystal growth by evaporation-induced convective steering Damien D. Brewer, Satish Kumar, Michael Tsapatsis We simulate evaporation-driven self-assembly of colloidal crystals using an equivalent network model. Relationships between a regular hexagonally close-packed array of hard, monodisperse spheres, the associated pore space, and selectivity mechanisms for face-centered cubic microstructure propagation are described. Accounting for contact line rearrangement and evaporation at a series of exposed menisci, the equivalent network model describes creeping flow of solvent into and through a rigid colloidal crystal. Observations concerning colloidal crystal growth are based on the convective steering hypothesis, which posits that solvent flow into and through the pore space of the crystal may play a major role in colloidal self-assembly. Aspects of the convective steering and deposition of high-Peclet-number rigid spherical particles at a crystal boundary are inferred from spatially resolved solvent flow into the crystal. Gradients in local flow through boundary channels were predicted due to the channels' spatial distribution relative to a pinned free surface contact line. When the free surface contact line is pinned near the leading crystal edge, the network simulations suggest that rows of particles preferentially nucleate furthest from the substrate. These lattice sites propagate the existing microstructure and lead to a declining shelf formation. [Preview Abstract] |
Tuesday, November 24, 2009 11:53AM - 12:06PM |
PU.00002: Motion of a spheroidal capsule in a simple shear flow Johann Walter, Anne-Virginie Salsac, Dominique Barth\`es-Biesel A capsule is a liquid droplet enclosed in a thin hyperelastic membrane. Microcapsules have various biomedical applications and can be studied as models for circulating cells, especially red blood cells. While many numerical studies have focussed on initially-spherical capsules, the aim of this work is to model the behavior of an ellipsoidal capsule in a simple shear flow. The capsule wall is modeled using finite membrane elements, while the fluids are treated using the boundary integral formulation of the Stokes equations. The viscosity ratio between the inner and outer fluids is kept at 1. When the membrane stiffness is large compared to the flow strength, the capsule undergoes a``tumbling'' motion. As the flow rate is increased, a transition occurs toward a ``swinging'' motion. In this study, we show the influence of the ellipticity of the capsule and of the law modeling the membrane on the behavior of the capsule. Aspect ratios ranging from $1:4$ (oblate) to $4:1$ (prolate) are considered, and two membrane laws (the neo-Hookean law and Skalak's) are compared. [Preview Abstract] |
Tuesday, November 24, 2009 12:06PM - 12:19PM |
PU.00003: Capillary oscillations and periodic defect formation in planar-flow spin casting of molten metal Brenton Cox, Paul Steen In the planar-flow casting process, surface tension holds liquid metal in a ``puddle'' where a thin ribbon is solidified as a product. Variations in the final thickness of the ribbon product are typically undesirable in manufacturing and are considered defects. Two similar periodic defects which appear in the ribbon product are studied and will be compared in this talk. The defect with wavelength $\lambda$ of order 1 mm appears at lower pressures. In higher pressure casts, the defect with $\lambda$ of order 10 mm appears. While the defect frequencies differ, they are found to scale with the same capillary/inertial time scale. It is observed experimentally that pinning/depinning on the upstream meniscus of the puddle determines which of the two defects will appear. When the upstream meniscus is pinned at the inlet aperture (constrained), the shorter wavelength defect appears. When the meniscus unpinned (free to move), the longer wavelength defect appears in the ribbon product. Instances in which the upstream meniscus may only partially pin due to imposed geometry of the inlet aperture result in coincidence of the two defects. [Preview Abstract] |
Tuesday, November 24, 2009 12:19PM - 12:32PM |
PU.00004: Dynamics of the capillary penetration of a viscous liquid into corrugated walls Fausto Sanchez, Abraham Medina, Francisco Higuera In this work we present a theoretical study of the spontaneous capillary flow, of a viscous liquid, developed into the gap between a couple of parallel corrugated plates (corrugated Hele- Shaw cell). The periodical corrugation of the interior walls of the plates is assumed as a sine-like pattern, transverse to the flow direction. Such a configuration may generate periodical gaps with a structure where zones of maximum and minimum closing occur. This is a simple idealization of typical micro and nano fabricated gaps used to mould polymers by capillarity. By using the lubrication theory we found that a very peculiar temporal flow is developed which could be of interest to improve the knowledge of this type of moulding. [Preview Abstract] |
Tuesday, November 24, 2009 12:32PM - 12:45PM |
PU.00005: Gas flows through shallow microchannel junctions and networks Amir Gat, Itzchak Frankel, Daniel Weihs We study creeping compressible (and incompressible) flows through micro-channel networks whose depth is small in comparison with all other dimensions. Making use of an extended Hele-Shaw asymptotic scheme together with conformal mapping we obtain the relation between the mass-flow-rate and the entrance and exit pressures of a T-junction, thereby quantifying the effects of the junction on the pressure field. The linearity of the problem in terms of an appropriately defined quadratic form of the pressure allows us to apply the results for a single junction towards the optimization of (inter-digitated) networks of parallel-micro-channels which include multiple T-junctions. [Preview Abstract] |
Tuesday, November 24, 2009 12:45PM - 12:58PM |
PU.00006: Numerical Study of the Buoyancy-Driven Flow in a Four-Electrode Rectangular Electrochemical Cell Zhanyu Sun, Vadim Agafonov, Catherine Rice, Jacob Bindler Two-dimensional numerical simulation is done on the buoyancy-driven flow in a four-electrode rectangular electrochemical cell. Two kinds of electrode layouts, the anode-cathode-cathode-anode (ACCA) and the cathode-anode-anode-cathode (CAAC) layouts, are studied. In the ACCA layout, the two anodes are placed close to the channel outlets while the two cathodes are located between the two anodes. The CAAC layout can be converted from the ACCA layout by applying higher electric potential on the two middle electrodes. Density gradient was generated by the electrodic reaction I$_{3}^{-}$+2e$^{-}$ =3I$^{-}$. When the electrochemical cell is accelerated axially, buoyancy-driven flow occurs. In our model, electro-neutrality is assumed except at the electrodes. The Navier-Stokes equations with the Boussinesq approximation and the Nernst-Planck equations are employed to model the momentum and mass transports, respectively. It is found that under a given axial acceleration, the electrolyte density between the two middle electrodes determines the bulk flow through the electrochemical cell. The cathodic current difference is found to be able to measure the applied acceleration. Other important electro-hydrodynamic characteristics are also discussed. [Preview Abstract] |
Tuesday, November 24, 2009 12:58PM - 1:11PM |
PU.00007: Drag Reduction of a Sphere by Ambient Perturbation and its Relationship with Stokes Layer Masaya Muto, Makoto Tsubokura, Nobuyuki Oshima An interaction between boundary layer of a sphere and equivalent Stokes layer generated by a perturbation in solid-air two-phase flow has been investigated using numerical simulation. In this simulation, the sphere is fixed in a cylindrical channel. Particle Reynolds number in this study is around 200 that means the wake of the sphere is steady and axisymmetric, and the friction drag and the pressure drag of the sphere are comparable. As a result of simulation, a drag reduction was found in a uniform flow with single-period perturbation oscillating in the same direction as the uniform flow when Stokes layer thickness is smaller than twice of boundary layer thickness in the sphere surface. A reason of the reduction of drag force is a reduction of friction drag caused by that fluctuation energy generated by the perturbation concentrates in the vicinity of particle and the time averaged velocity gradient becomes smaller. [Preview Abstract] |
Tuesday, November 24, 2009 1:11PM - 1:24PM |
PU.00008: The Complex Nature of Turbulence Transition in Boundary Layer Flow Jim Chen, Chen Weijia Turbulence transition is the process where a laminar field evolves to become turbulent, signaled by the presence of random oscillations. To fully understand turbulence transition demands thoughtful and interconnected consideration of three elements that describe its nature, its physics, mathematics, and numerical simulation. They are interdependent, mutually illuminating elements that form a problem of awe-inspiring complexity. They also examine the problem from a spectrum of perspectives. First, a far-sighted perspective is needed that views the overall problem in its macroscopic, general terms such as its experimental settings, governing equations and boundary conditions. Accompanying it is a precision-oriented, detail-solicitous view of minute, microscopic intricacies such as small-scale turbulence vortices and infinitesimal instability wave interactions that transpire in the flow. The capacity and tolerance to switch between varying degrees of these orthogonally-oriented perspectives is necessary to systematically break down this problem. This study demonstrates a deconstruction of the phenomenon of turbulence transition in order to gain an appreciation of its very complex nature. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700