Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session Y8: General Fluid Dynamics |
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Sponsoring Units: DFD Chair: John Labenski, National Institute of Standards and Technology Room: Baltimore Convention Center 314 |
Friday, March 17, 2006 8:00AM - 8:36AM |
Y8.00001: DCOMP Award Lecture (Metropolis): A 3D Spectral Anelastic Hydrodynamic Code for Shearing, Stratified Flows Invited Speaker: We have developed a three-dimensional (3D) spectral hydrodynamic code to study vortex dynamics in rotating, shearing, stratified systems (eg, the atmosphere of gas giant planets, protoplanetary disks around newly forming protostars). The time-independent background state is stably stratified in the vertical direction and has a unidirectional linear shear flow aligned with one horizontal axis. Superposed on this background state is an unsteady, subsonic flow that is evolved with the Euler equations subject to the anelastic approximation to filter acoustic phenomena. A Fourier-Fourier basis in a set of quasi-Lagrangian coordinates that advect with the background shear is used for spectral expansions in the two horizontal directions. For the vertical direction, two different sets of basis functions have been implemented: (1) Chebyshev polynomials on a truncated, finite domain, and (2) rational Chebyshev functions on an infinite domain. Use of this latter set is equivalent to transforming the infinite domain to a finite one with a cotangent mapping, and using cosine and sine expansions in the mapped coordinate. The nonlinear advection terms are time integrated explicitly, whereas the Coriolis force, buoyancy terms, and pressure/enthalpy gradient are integrated semi- implicitly. We show that internal gravity waves can be damped by adding new terms to the Euler equations. The code exhibits excellent parallel performance with the Message Passing Interface (MPI). As a demonstration of the code, we simulate vortex dynamics in protoplanetary disks and the Kelvin-Helmholtz instability in the dusty midplanes of protoplanetary disks. [Preview Abstract] |
Friday, March 17, 2006 8:36AM - 8:48AM |
Y8.00002: Evaporating droplets Noushine Shahidzadeh-Bonn, Salima Rafai, Aza Azouni, Daniel Bonn In our everyday life we are constantly confronted with evaporating drops and the consequences of it. The seemingly simple problem of an evaporating droplet has attracted a great deal of attention over the past years. The problem is complicated due to the fact that the form of the droplet during the evaporation is a priori unknown, and due to the large number of effects that have to be taken into account (temperature, convection, Marangoni effects{\ldots}). We consider the very simple situation of the evaporation of a perfectly wetting liquid on a molecularly smooth surface. The radius R(t) of the droplet is followed in time until it reaches zero. If the evaporation is purely diffusive, a radius that decreases as the square root of time is expected; this is indeed found for organic liquids, but water has a different exponent. We show that the difference is likely to be due to the fact that water vapor is lighter than air, and the vapor of other liquids more dense. If we carefully confine the water so that the diffusive boundary layer may develop, we retrieve the square root of time behavior. On the other hand, if we force convection for an organic liquid, we retrieve the anomalous exponent for water. [Preview Abstract] |
Friday, March 17, 2006 8:48AM - 9:00AM |
Y8.00003: Effect of Viscoelasticity on Drop Deformation Nishith Aggarwal, Kausik Sarkar Deformation of a drop is numerically investigated when one or both of the drop and continuous phases is viscoelastic. A three-dimensional front-tracking finite difference method is used to simulate the deforming drop. The viscoelasticity is modeled using the Giesekus and Oldroyd--B constitutive relations. In a shear flow, a viscoelastic drops in a Newtonian matrix deforms less than a Newtonian drop. Specifically, bounded viscoelastic drop shapes are found for capillary numbers where a Newtonian drop would break up. Matrix viscoelasticity, however is observed to cause non-monotonic change in drop deformation with increasing viscoelasticity. The effects of inertia, interfacial tension, viscosity ratio and imposed flow periodicity (in oscillatory shear) will be presented. The detailed results about transient dynamics, viscous and viscoelastic stresses and the velocity fields inside and outside the drop will be discussed and explained. [Preview Abstract] |
Friday, March 17, 2006 9:00AM - 9:12AM |
Y8.00004: Pressure Driven Liquid-Vapor Phase Transitions Tianshi Lu, Roman Samulyak, James Glimm Liquid-vapor phase transitions driven by pressure waves have been studied analytically and numerically. The Stefan problem has been extended to incorporate the compressibility of the vapor phase. Both internal heat conduction and external heat deposition (such as from electrons in tokamak fusion reactors) have been considered. The steady state and the transient waves in the phase transitions have been investigated. A numerical scheme has been developed for the simulation of compressible two-phase flows with phase transitions in the frame of front tracking. Phase boundaries can be created dynamically in regions under critical conditions. The numerical method has been applied to the simulation of boiling and cavitating processes. [Preview Abstract] |
Friday, March 17, 2006 9:12AM - 9:24AM |
Y8.00005: Interaction between a free boundary and thermal convection in an annulus Jin-Qiang Zhong, Jun Zhang We report an experimental study in turbulent thermal convection that has a free upper surface. The geometry of the convective system is annular with aspect ratio (girth/height) 6.8 and with periodic boundary condition. Our experiment studies the interaction between the convective flow and a freely moving floating boundary that partially covers the open surface. The floating boundary position and the corresponding convective pattern are recorded at the same time and are correlated to reveal the dynamics of the coupled system. Our experiment aims to illustrate the intricate mechanism of continental drift that is driven by mantle convection. [Preview Abstract] |
Friday, March 17, 2006 9:24AM - 9:36AM |
Y8.00006: The Stochastic Dynamics of an Array of Atomic Force Microscope Cantilevers in a Viscous Fluid Matthew Clark, Mark Paul The hydrodynamic coupling between micron scale atomic force microscope cantilevers in a viscous fluid is studied. Using the fluctuation-dissipation theorem, the stochastic dynamics of the cantilevers are quantified from deterministic calculations. Numerical simulations of individual cantilevers immersed in fluid are used to verify the approach. A simple harmonic oscillator model is shown to be reasonable for the description of the dynamics of a single cantilever. The fluid induced correlations in an array of cantilevers are then explored and quantified. Absolute predictions of the cross-correlations in the equilibrium fluctuations of cantilever displacement are presented. This is used to yield limits of the force and time scales of operation for a correlation detection method using multiple atomic force microscope cantilevers. [Preview Abstract] |
Friday, March 17, 2006 9:36AM - 9:48AM |
Y8.00007: Co-rotating Batchelor vortex merging Paulo Ferreira de Sousa, Jose Carlos Fernandes Pereira The dynamics of co-rotating vortex pairs without axial flow has been recently thoroughly studied through theoretical, experimental and numerical studies, which revealed different instabilities contributing to the decay of the vortices. In this paper the objective is to extend the analysis to the case of co-rotating vortices with axial flow at low Reynolds numbers. A high-order incompressible Navier-Stokes flow solver is used. The momentum equations are spatially discretized on a staggered mesh by finite differences and all derivatives are evaluated with 4th order compact finite difference schemes with RK-4 temporal discretization. The initial condition is a linear superposition of two co-rotating circular Batchelor vortices with q = 1. It is found that there is an initial evolution that resembles the evolution that single q = 1 vortices go through. Azimuthal disturbances grow and result in the appearance of large-scale helical sheets of vorticity. With the development of these instability waves, the axial velocity deficit is weakened. The redistribution of both angular and axial momentum between the core and the surroundings drives the vortex core to a more stable configuration, with a higher q value. After these processes, the evolution is somewhat similar to a pair of co-rotating Lamb-Oseen vortices. A three-dimensional instability develops, with a large band of unstable modes, with the most amplified mode corresponding scaling with the vortex initial separation distance. [Preview Abstract] |
Friday, March 17, 2006 9:48AM - 10:00AM |
Y8.00008: Magnetic Body Force Sustained Temperature Gradient Jonathan Fraine, Weili Luo The temperature gradient was established in a magnetic fluid by controlling the rate of cycling coolant. Measurements were done to monitor temperature gradient verses time before and after the cooling was stopped in both zero and applied magnetic field. We found that the magnetic field can sustain a larger temperature gradient. The theoretical calculation shows that the effect of field on the temperature gradient is attributed to the magnetic body force that depends on the gradient of the susceptibility. [Preview Abstract] |
Friday, March 17, 2006 10:00AM - 10:12AM |
Y8.00009: Shock Interaction with a Finite Thickness Two-Gas Interface John Labenski, Yong Kim A dual-driver shock tube was used to investigate the growth rate of a finite thickness two-gas interface after shock forcing. One driver was used to create an argon-refrigerant interface as the contact surface behind a weak shock wave. The other driver, at the opposite end of the driven section, generates a stronger shock of Mach 1.1 to 1.3 to force the interface back in front of the detector station. Two schlieren systems record the density fluctuations while light scattering detectors record the density of the refrigerant as a function of position over the interface during both it's initial passage and return. A pair of digital cameras take stereo images of the interface, as mapped out by the tracer particles under illumination by a Q-switched ruby laser. The amount of time that the interface is allowed to travel up the driven section determines the interaction time as a control. Comparisons made between the schlieren signals, light scattering detector outputs, and the images quantify the fingered characteristics of the interface and its growth due to shock forcing. The results show that the interface has a distribution of thicknesses and that the interaction with a shock further broadens the interface. [Preview Abstract] |
Friday, March 17, 2006 10:12AM - 10:24AM |
Y8.00010: Investigation of Oxygen Transfer Enhancement in Thermally Driven Cavities By Lattice Boltzmann Simulation. Huidan Yu, Jinsuo Zhang, Ning Li We investigate the enhancement of mass transfer in 2D thermally driven cavities using lattice Boltzmann equation (LBE) method. The computational technique integrates three coupled LBEs for solving velocity, temperature, and concentration fields simultaneously. Simulation is performed for oxygen transfer in lead/lead-bismuth eutectic with variations of temperature boundary, Schmidt number, and field aspect ratio to investigate the effects on enhancement of oxygen transfer. Interested characteristics include oxygen concentration, Sherwood number, and velocity profiles, etc. Our results clearly indicate that oxygen transfer is dominated by convection while diffusion also plays a role on it. Comparative studies demonstrate that side heating and top cooling device is more efficient to transfer oxygen than side heating and cooling device and oxygen transfers more rapidly in square cavity than in rectangular cavity. This work establishes a reliable thermal LBE model for thermally driven heat and mass transfer. [Preview Abstract] |
Friday, March 17, 2006 10:24AM - 10:36AM |
Y8.00011: Energy from Ocean Waves, River Currents, and Wind Shyamal Guha The Earth we live in is surrounded by fluids, which are in perpetual motion. The air in the atmosphere and water found in lakes, ocean, and rivers form our natural environment. Much of the fluid medium is in constant motion. The kinetic energy of this moving fluid is astronomical in magnitude. Over the years, I have considered methods of converting a fraction of the vast reserve of this kinetic energy into electro-mechanical energy. I have conceived a few schemes of such conversions. The fluids whose kinetic energy can be converted into electro-mechanical energy are the following: ocean waters, river currents and atmospheric air. In a book to be published in the spring of 2006, I have described different techniques of energy conversion. In the upcoming APS meeting, I plan to discuss some of these techniques. [Preview Abstract] |
Friday, March 17, 2006 10:36AM - 10:48AM |
Y8.00012: Motion of Rigid Bodies in Newtonian and non-Newtonian Fluids Ashwin Vaidya The properties of non-Newtonian fluids, such as normal stress effects and non-constant viscosities are known to result in flow phenomenon which are dramatically different from those of Newtonian fluids. One such interesting difference in the behavior of these kinds of fluids is in their interaction with submerged rigid bodies. In this talk, we will focus on the problem of steady motions of symmetric rigid bodies as they freefall in Newtonian and viscoelastic fluids, modeled by the Navier Stokes, Power Law, Second order and the Generalized Second order fluid models. We will examine how variations in forces and torques in these two kinds of fluids can result in remarkably different phenomenon. [Preview Abstract] |
Friday, March 17, 2006 10:48AM - 11:00AM |
Y8.00013: Particle Dynamics in Low Reynolds Number Fluidized Beds Phil Segre, Jim McClymer The sedimentation dynamics of extremely low polydispersity, $\sigma_a/a \sim 1.5\%$, non-Brownian, particles are studied in a liquid fluidized bed at low Reynolds number, $Re\ll 1$. When fluidized, the system reaches a steady state in which the local velocity fluctuations and particle concentration are found to become highly stratified with height in the column. Results are presented for the degree of stratification with normalized bed height $H/a$. We find that taller beds are more stratified than shorter beds. However, recent computer simulations have not found any measurable stratification with height. We reconcile this apparent disagreement by showing that the stratification in experiments of comparably small systems such as those studied by simulation are indeed very small. We also develop a simple advection-diffusion model that connects the velocity fluctuations to the concentration gradients, and account for the observed bed stability. [Preview Abstract] |
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