Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session NR: Suspensions II |
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Chair: Howard Hu, University of Pennsylvania Room: Salt Palace Convention Center 251 F |
Tuesday, November 20, 2007 11:35AM - 11:48AM |
NR.00001: Particle Accumulation At An Advancing Interface In Dense Suspension Flow Timothy Singler, John Molyneux It is well known that the volume fraction of particles adjacent to a meniscus formed by a dense suspension in contact with another immiscible fluid increases if the meniscus is advancing and decreases if the meniscus is receding. Particle accumulation at an advancing interface has been observed in tubes and narrow-gap flows and has been suggested to induce an instability in the latter case. Only ad hoc explanations of the accumulation phenomenon have been offered. We analyze the flow of a dense suspension in the gap of a rectangular Hele Shaw cell with a simple model of the advancing interface and solve the 2-D phenomenological equations for the suspension that provide for hydrodynamic diffusion of the particles. The equation set is solved using a finite volume methodology. The flow domain is a two dimensional rectangle with prescribed inflow and concentration at the base. The upper boundary, representing a free surface with an essentially inviscid fluid, is modeled for simplicity as a rigid free-slip lid that moves so as to maintain mass conservation. The results from this simple computational model will be compared with experiment. [Preview Abstract] |
Tuesday, November 20, 2007 11:48AM - 12:01PM |
NR.00002: Effects of electric fields on the rheological properties of emulsions of drops Arturo Fernandez The results of fully three-dimensional direct numerical simulations of the effects of electric fields on emulsions of drops will be presented. The examination of the rheological properties of these systems is performed by imposing a simple- shear flow between two plates where the drops are immersed. An electric potential difference is applied perpendicular to the plates. The resulting electric field leads to two effects: a polarization of the drops and a viscous fluid motion on the interface between the drops and the suspending fluid. The direction and intensity of the viscous fluid motion depends on the electrical properties of the fluids. The numerical simulations show that the response of the emulsions is governed by the competition between the electric attraction and the fluid shear. The former leads to the aggregation of the drops in chains parallel to the electric field, while the latter tries to break-up the aggregated chains. The results are presented as a function of the Mason number and the electric capillary numbers. These non-dimensional numbers quantify the strength of the electric forces versus the fluid shear and the capillary forces, respectively. The significance of the electrical field on the viscosity and the normal stress differences will be discussed. [Preview Abstract] |
Tuesday, November 20, 2007 12:01PM - 12:14PM |
NR.00003: Lattice Boltzmann Simulation of Directed Assembly in Nano-Colloidal Systems Mohammad Abuzaid, Ying Sun Suspensions of nano-sized colloids have received great attention for their broad applications in printable electronics, photonics, thin film processing, thermal management, etc. The properties of colloidal suspensions are often influenced by the interplay of the electrostatic repulsion, van der Waals attraction, depletion forces, hydrodynamic interaction, Brownian motion, diffusion, and gravity. In many applications, it is desirable to have ordered nanostructures, which can be achieved by electro-hydrodynamically directed particle assembly. In this paper, a Lattice Boltzmann scheme is used for direct numerical simulation of particle-particle and particle-field interactions in nano-colloidal systems under flow and electric fields. The interaction between particles and fluid is simulated via a mass conserving second-order bounce-back scheme. The aggregation rate of colloidal suspensions is investigated as a function of the fluid velocity and pressure, electric potential, electrode geometry, particle size and volume fraction, temperature, sedimentation effect, and other properties of both the particles and the carrier fluid. The influence of colloid size on various interaction forces is examined in detail. The design protocols for tuning colloidal suspensions under different electro-hydrodynamic field conditions are discussed for nanocrystalline thin film processing and nanofluids for thermal management. [Preview Abstract] |
Tuesday, November 20, 2007 12:14PM - 12:27PM |
NR.00004: Rayleigh-Taylor Instability in a Sedimenting Suspension Peter Mucha, Swathi Guda The evolution of the unstable interface between particles sedimenting under gravity above and clear fluid below is investigated computationally. Large numbers of model particles undergoing dilute hydrodynamic interactions between no-slip side walls are simulated under various physical and numerical parameters. Growth rates for different wave numbers characterizing the initial instabilities in the developing front are calculated and compared favorably with results for miscible fluids and with existing experimental and computational results in the literature. A model visualization technique is applied to the simulated data to further investigate the hydrodynamic mechanisms involved, both in the initial instability and in the evolution of particle-laden fingers. This talk includes joint work with Svetlana Bukharina, Florian Hecht, and Greg Turk. [Preview Abstract] |
Tuesday, November 20, 2007 12:27PM - 12:40PM |
NR.00005: Effect of Particle Deformation on Suspension Rheology using a Hybrid Lattice-Boltzmann -- Finite Element Method Jonathan Clausen, Robert MacMeccan, Cyrus Aidun Many suspensions contain particles where the deformation of the solid phase significantly alters the behavior of the flow. In the present study, the effect of particle deformation on suspension rheology is quantified using a novel simulation technique which couples the lattice-Boltzmann method for the fluid phase to finite-element analysis for the solid phase. Simulations of three-dimensional deformable particles in simple shear are presented with emphasis on the effect particle deformation has on suspension rheology. Effective viscosity and normal stress differences are analyzed in high concentration suspensions of up to 400 particles. The results include simulation of red blood cells at physiologic concentrations and comparison to spherical capsules with similar material properties. [Preview Abstract] |
Tuesday, November 20, 2007 12:40PM - 12:53PM |
NR.00006: Collective dynamics in suspensions bounded by two planar walls via a new accelerated Stokesian-dynamics algorithm Jerzy Blawzdziewicz, Eligiusz Wajnryb Our novel accelerated Stokesian-dynamics algorithm for a system of spherical particles bounded by two parallel planar walls serves to efficiently follow the dynamics of about $10^3$ particles. Its high efficiency is due to simplifications associated with the far-field asymptotics of the scattered flow produced by the particles. By a proper choice of basis Stokes flows (which in the near field tend to Lamb solutions and in the far field to multipolar basis of Hele-Shaw flows), the problem is reduced to a sparse linear system that is solved at a low numerical cost using iterative sparse-matrix manipulation techniques. We also present applications of our algorithm to study suspension transport in microfluidic channels and collective motion of large regular particle arrays in Poiseuille flow. [Preview Abstract] |
Tuesday, November 20, 2007 12:53PM - 1:06PM |
NR.00007: Simulation of Motion and Deformation of Elastic Objects in Flows Howard Hu We present a numerical technique that simulates the dynamics of flexible bodies in moving fluids. We are interested in studying the motion and deformation of elastic particles, for example biological cells, which are flexible and liable to undergo large deformations along with translation and rotation. Our numerical technique uses the moving mesh finite element method to solve the initial value problem of moving objects. The movement and the deformation of the objects are handled with an Arbitrary Lagrangian Eulerian (ALE) scheme. The numerical scheme solves the equations of motion for an incompressible elastic solid (with non-linear strain tensor) inside the particles, and those for Newtonian fluids for the liquid phase. The coupling between the solid and liquid phase is enforced by assuming that the material velocity and the stress are continuous across the interface between the solid and the liquid. In addition, the displacement field inside the particles is solved, and its gradient in the form of Almansi strain tensor is used to evaluate the stress inside the particles. This numerical scheme is demonstrated to be stable and is capable to resolve large deformations of the particles. [Preview Abstract] |
Tuesday, November 20, 2007 1:06PM - 1:19PM |
NR.00008: Direct simulations of spherical particle suspensions in a sliding tri-perioidic cell Wook Ryol Hwang, Martien A. Hulsen, Tai Hun Kwon, Han E.H. Meijer We present a finite-element/fictitious-domain scheme for 3D direct simulations of suspensions of spherical particles in a Newtonian fluid in simple shear flow in a tri-periodic computational domain, which is a 3D extension of the authors' previous 2-D work [J. Comput. Phys. 194 (2004) 742]. The sliding tri-periodic cell, where suspensions in an unbounded domain in simple shear may be treated by a representative particulate problem in a unit cell, has been implemented with the mortar element method. The force-free torque-free rigid body motion of ta spherical particle is described by the rigid-shell description and implemented by Lagrangian multipliers only on the particle boundary. The bulk stress is obtained by simple boundary integrals. Through the several example problems, we discuss the the rheological properties of the bulk shear viscosity and the first/second normal stress coefficients. [Preview Abstract] |
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