Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session M9: General Fluid Dynamics: Viscous Flows |
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Chair: Randy Ewoldt, University of Illinois, Urbana-Champaign Room: B117 |
Tuesday, November 22, 2016 8:00AM - 8:13AM |
M9.00001: A validated computational model for the design of surface textures in full-film lubricated sliding Jonathon Schuh, Yong Hoon Lee, James Allison, Randy Ewoldt Our recent experimental work showed that asymmetry is needed for surface textures to decrease friction in full-film lubricated sliding (thrust bearings) with Newtonian fluids; textures reduce the shear load and produce a separating normal force. The sign of the separating normal force is not predicted by previous 1-D theories. Here we model the flow with the Reynolds equation in cylindrical coordinates, numerically implemented with a pseudo-spectral method. The model predictions match experiments, rationalize the sign of the normal force, and allow for design of surface texture geometry. To minimize sliding friction with angled cylindrical textures, an optimal angle of asymmetry $\beta$ exists. The optimal angle depends on the film thickness but not the sliding velocity within the applicable range of the model. The model has also been used to optimize generalized surface texture topography while satisfying manufacturability constraints. [Preview Abstract] |
Tuesday, November 22, 2016 8:13AM - 8:26AM |
M9.00002: Viscous erosion at low Reynolds number William Mitchell, Saverio Spagnolie We study the shape evolution of immersed particles in a viscous fluid under several flow configurations, including uniform background flows and shear flows in wall-bounded or free domains. The surface recedes proportionally to local shear stress, which we compute using a new traction integral formulation of Newtonian Stokes flow. This opens the door to efficient numerical simulation of the evolving particle geometry. Analytical predictions from reduced-order models are then compared against the numerical simulations. For the case of particles held fixed against an oncoming background flow, the theory predicts the finite time required for complete particle dissolution as well as the emergence and locations of sharp corners on the eroding bodies. Simulations involving force- and torque-free particles and multibody systems are also presented. [Preview Abstract] |
Tuesday, November 22, 2016 8:26AM - 8:39AM |
M9.00003: Measurement of steady and transient liquid coiling with high-speed video and digital image processing Frank Austin Mier, Raj Bhakta, Nicolas Castano, Joshua Thackrah, Tyler Marquis, John Garcia, Michael Hargather Liquid coiling occurs as a gravitationally-accelerated viscous fluid flows into a stagnant reservoir causing a localized accumulation of settling material, commonly designated as stack. This flow is broadly characterized by a vertical rope of liquid, the tail, flowing into the stack in a coiled motion with frequency defined parametrically within four different flow regimes. These regimes are defined as viscous, gravitational, inertial-gravitational, and inertial. Relations include parameters such as flow rate, drop height, rope radius, gravitational acceleration, and kinematic viscosity. While previous work on the subject includes high speed imaging, only basic and often averaged measurements have been taken by visual inspection of images. Through the implementation of additional image processing routines in MATLAB, time resolved measurements are taken on coiling frequency, tail diameter, stack diameter and height. Synchronization between a high speed camera and stepper motor driven syringe pump provides accurate correlation with flow rate. Additionally, continuous measurement of unsteady transition between flow regimes is visualized and quantified. This capability allows a deeper experimental understanding of processes involved in the liquid coiling phenomenon. [Preview Abstract] |
Tuesday, November 22, 2016 8:39AM - 8:52AM |
M9.00004: Angular dynamics of small crystals in viscous flows Johan Fries, Jonas Einarsson, Bernhard Mehlig The angular dynamics of a very small ellipsoidal particle in a viscous flow decouples from its translational dynamics, and the particle angular velocity is given by Jeffery’s theory. It is known that cuboid particles share these properties. In the literature a special case is most frequently discussed, that of axisymmetric particles, with a continuous rotational symmetry. Here we compute the angular dynamics of crystals that possess a discrete rotational symmetry and certain mirror symmetries, but that do not have a continuous rotational symmetry. We give examples of such particles that nevertheless obey Jeffery’s theory. But there are other examples where the angular dynamics is determined by a more general equation of motion. [Preview Abstract] |
Tuesday, November 22, 2016 8:52AM - 9:05AM |
M9.00005: Reverse Fluid Transport Due to Boundary Pulsations Mikhail Coloma, David Schaffer, Paul Chiarot, Peter Huang We investigate a reverse fluid transport mechanism consisting of peristaltic flow and boundary wave reflections. The reverse flow occurs in a rectangular conduit aligned in parallel between two cylindrical channels embedded in an elastic PDMS medium. The pulsating flow in the cylindrical channels, driven by a peristaltic pump, deform the PDMS medium and induce a pulsating flow in the rectangular conduit. Waveforms along the conduit boundaries, and their transmission and reflections, can be controlled by changing the PDMS rigidity. Our results show that while the overall wave propagation direction is in the forward direction, a reverse flow in the rectangular conduit can be preferentially induced by varying the elastic rigidity in one of the cylindrical channels. We study the overall flow velocity and direction under various PDMS rigidities. The identified set of experimental parameters that leads to a reverse flow will provide insights in understanding metabolic waste transport within the arterial walls in the brain. [Preview Abstract] |
Tuesday, November 22, 2016 9:05AM - 9:18AM |
M9.00006: Oscillatory slip flow past a spherical inclusion embedded in a Brinkman medium D. Palaniappan Non-steady flow past an impermeable sphere embedded in a porous medium is investigated based on Brinkman model with Navier slip conditions. Exact analytic solution for the stream-function - involving modified Bessel function of the second kind - describing the slow oscillatory flow around a rigid spherical inclusion is obtained in the limit of low-Reynolds-number. The key parameters such as the frequency of oscillation $\lambda$, the permeability constant $\delta$, and the slip coefficient $\xi$ control the flow fields and physical quantities in the entire flow domain. Local streamlines for fixed times demonstrate the variations in flow patterns. Closed form expressions for the tangential velocity profile, wall shear stress, and the force acting on the sphere are computed and compared with the existing results. It is noted that the slip parameter in the range $0\le\xi\le0.5$ has a significant effect in reducing the stress and force. The steady-state velocity overshoot behavior in the vicinity of the sphere is re-iterated. In the limit of large permeability, Darcy (potential) flow is recovered outside a boundary layer. The results are of some interest in predicting maximum wall stress and pressure drop associated with biological models in fibrous media. [Preview Abstract] |
Tuesday, November 22, 2016 9:18AM - 9:31AM |
M9.00007: Buckling and stretching of thin viscous sheets Doireann O'Kiely, Chris Breward, Ian Griffiths, Peter Howell, Ulrich Lange Thin glass sheets are used in smartphone, battery and semiconductor technology, and may be manufactured by producing a relatively thick glass slab and subsequently redrawing it to a required thickness. The resulting sheets commonly possess undesired centerline ripples and thick edges. We present a mathematical model in which a viscous sheet undergoes redraw in the direction of gravity, and show that, in a sufficiently strong gravitational field, buckling is driven by compression in a region near the bottom of the sheet, and limited by viscous resistance to stretching of the sheet. We use asymptotic analysis in the thin-sheet, low-Reynolds-number limit to determine the centerline profile and growth rate of such a viscous sheet. [Preview Abstract] |
Tuesday, November 22, 2016 9:31AM - 9:44AM |
M9.00008: A reciprocal theorem for convective heat and mass transfer in Stokes and potential flows Hassan Masoud, Vahid Vandadi, Saeed Jafari Kang In the study of convective heat and mass transfer from a particle, key quantities of interest are usually the average rate of transfer and the mean distribution of the scalar (i.e., temperature or concentration) at the particle surface. Calculating these quantities using conventional equations requires detailed knowledge of the scalar field, which is available predominantly for problems involving uniform scalar and flux boundary conditions. Here, we derive a reciprocal relation between two diffusing scalars that are advected by oppositely driven Stokes or potential flows whose streamline configurations are identical. This relation leads to alternative expressions for the aforementioned average quantities based on the solution of the scalar field for uniform surface conditions. [Preview Abstract] |
Tuesday, November 22, 2016 9:44AM - 9:57AM |
M9.00009: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2016 9:57AM - 10:10AM |
M9.00010: ABSTRACT WITHDRAWN |
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