Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A23: General Fluid Dynamics: Viscous FlowsGeneral
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Chair: Hassan Masoud, Michigan Technological University Room: 710 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A23.00001: Heat transfer from a particle in creeping flow of a variable-conductivity fluid Esmaeil Dehdashti, Meghdad Razizadeh, Hassan Masoud We revisit the classical problem of heat transfer from a single particle in a uniform Stokes flow with the assumption that the fluid conductivity changes linearly with the temperature. We use a combination of asymptotic analysis and numerical simulation to derive semi-analytical expressions for the dimensionless heat transfer coefficient, i.e. Nusselt number (Nu), of spheroidal particles. The results cover the entire range of Peclet number (Pe). We find that, for a constant temperature boundary condition and fixed geometry, the Nusselt number is essentially equal to the product of two terms, one of which is only a function of Pe while the other one is nearly independent of Pe and mainly depends on the proportionality constant of the conductivity-temperature relation. We also show that, in contrast, when a uniform heat flux is imposed on the surface of the particle, Nu can be written as a summation of a Pe dependent piece and one that solely varies with the proportionality constant. Finally, we discuss the extension of these results to non-spheroidal particles and to finite-Reynolds-number flows. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A23.00002: Dynamics of knotted flexible loops settling under a constant force in a viscous fluid Magdalena Gruziel, Krishnan Thyagarajan, Giovanni Dietler, Piotr Szymczak, Maria Ekiel-Jezewska Sedimenting chains of metal beads knotted to a topology of a torus knot tend to stabilize in the form of extended, flat, tightly interwound loops. In this configuration they perform an oscillatory motion of the loops swirling periodically around each other. Stokesian dynamics simulations of elastic fibers confirm the longlasting character of the traveling wavelike swirling motion and show also the accompanying rotation of the system. Moreover, the periodic motion shows striking resemblance to the stable solutions for the evolution of vortices of torus knot topology. Using the results of the simulations we study the dependence of the frequencies and sedimentation velocities on the length of the fiber. We also notice the dependence of the knot dynamics on the bending stiffness of the fiber and the knot rank. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A23.00003: A shocking viscous gravity current Frederik Dauck, John Lister We analyse propagation of a viscous gravity current over a layer of different fluid, but with the same density. Exact similarity solutions are found with two free parameters: a non-dimensional flux $Q$ and the viscosity ratio $m$. The theory predicts a jump discontinuity, or shock, at the nose of the current for $m>m_{crit}$, which develops kinematically due to the hyperbolic nature of the interfacial height equation. The jump is identified as a novel form of under-compressive shock, resulting from a non-concave relative flux function and the total height variations. Small non-zero density differences regularise this system, and a local travelling-wave solution near the nose justifies the shock conditions for the jump height as a function of $m$. Our results obtained compare well to experimental data, both in terms of the predictions of radial extent and of the overall shape. In some circumstances, the front becomes unstable. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A23.00004: Highly-viscous microjet induced by an impact Hajime Onuki, Yoshiyuki Tagawa Ejection of a liquid microjet with high viscosity is essential for various novel technologies such as 3D printers, printed electronics and bio printers. To generate such a microjet, we focus on utilizing an impulsive force. Thanks to a short-time impact, the viscous dissipation in the liquid can be suppressed, resulting in the ejection of viscous microjets. In this study, we investigate ejection mechanism of the viscous jet experimentally and numerically. The jet velocity decreases with increasing the viscosity of a liquid. Remarkably it is found that all the data of jet velocities normalized by initial velocities of the liquid as a function of Reynolds number, the balance between the inertia force and the viscous force, collapse onto a single master curve. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A23.00005: Loss Prediction of Low Re Flow Through Quasiperiodic Serpentine Channels Sid Becker Low Re internal flow through a complex structure whose geometry is regular (periodically uniform) will experience losses that are periodically regular and may be predicted using simple correlations. In many porous media applications this is represented by Darcy's Law. This study considers the prediction of losses through a channel whose geometry is periodic but with characteristic length scales that vary in the direction of bulk flow. Asymptotic expansions of the variation in the characteristic length are implemented in flow simulations in order to determine a correlation relating local hydraulic permeability to local channel geometry. In this way the local losses may be predicted without requiring the explicit solution of the flow field for every specific channel geometry. Several test cases are presented showing that using these correlations, the local pressure losses may predicted to within 0.5{\%} agreement with the solution to the Navier-Stokes Equations. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A23.00006: Stokes flow in a channel-polygonal geometry Elena Luca, Stefan Llewellyn Smith Motivated by modelling challenges arising in microfluidics, we consider low-Reynolds-number flow in a two-dimensional channel with different widths in the upstream and downstream directions. The channel geometry is approximated by a polygonal domain with angled edges at `transition' points. We consider a pressure-driven flow with different inlet and outlet velocities related via the flux balance condition and obtain semi-analytical solutions using new transform methods. Our aim is to examine how different parameter choices affect the resulting flow as well as compute the pressure field everywhere in the flow domain. [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A23.00007: Gaseous Viscous Peeling of Linearly Elastic Substrates Shai Elbaz, Hila Jacob, Amir Gat We study pressure-driven propagation of gas into a micron-scale gap between two linearly elastic substrates. Applying the lubrication approximation, the governing nonlinear evolution equation describes the interaction between elasticity and viscosity, as well as weak rarefaction and low-Mach-number compressibility, characteristic to gaseous microflows. Several physical limits allow simplification of the evolution equation and enable solution by self-similarity. During the peeling process the flow-field transitions between the different limits and the respective approximate solutions. The sequence of limits occurring during the propagation dynamics can be related to the thickness of the prewetting layer of the configuration at rest, yielding an approximate description of the entire peeling dynamics. The results are validated by numerical solutions of the evolution equation. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A23.00008: Deformations of a pre-stretched and lubricated finite elastic membrane driven by non-uniform external forcing Evgeniy Boyko, Amir Gat, Moran Bercovici We study viscous-elastic dynamics of a fluid confined between a rigid plate and a finite pre-stretched circular elastic membrane, pinned at its boundaries. The membrane is subjected to forces acting either directly on the membrane or through a pressure distribution in the fluid. Under the assumptions of strong pre-stretching and small deformations of the elastic sheet, and by applying the lubrication approximation for the flow, we derive the Green's function for the resulting linearized 4th order diffusion equation governing the deformation field in cylindrical coordinates. In addition, defining an asymptotic expansion with the ratio of the induced to prescribed tension serving as the small parameter, we reduce the coupled Reynolds and non-linear von-Karman equations to a set of three one-way coupled linear equations. The solutions to these equations provide insight onto the effects of induced tension, and enable simplified prediction of the correction for the deformation field. [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A23.00009: Dynamics of Solid-Liquid Composite Beams Yoav Matia, Amir Gat Solid-liquid composite structures received considerable attention in recent years in various fields such as smart materials, sensors, actuators and soft-robotics. We examine a beam-like appendage embedded with a set of a fluid-filled bladders, interconnected via elastic slender channels; a common arrangement in the abovementioned fields. Viscous flow within such structures is coupled with the elastic deformation of the solid. Beam deformation both creates, and is induced by, a fluidic pressure gradient and viscous flow which deforms the bladders and thus the surrounding solid. Applying concepts from poroelastic analysis, we obtain a set of three interdependent equations relating the fluidic pressure within the channel to the transverse and longitudinal displacements of the beam. Exact and approximate solutions are presented for various configurations. The results are validated and supplemented by a transient three-dimensional numerical study of the fluid-structure-interaction. The two-way coupled fluid-structure-interaction model allows the analysis and design of soft smart-metamaterials with unique mechanical properties, to applications such as touch-sensing surfaces, energy harvesting and protective gear. [Preview Abstract] |
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