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 LT: Suspensions I |
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Chair: David Saintillan, University of Illinois at Urbana-Champaign Room: 200H |
Monday, November 23, 2009 3:35PM - 3:48PM |
LT.00001: Near-wall colloidal dynamics probed by evanescent-wave dynamic light scattering J. Blawzdziewicz, E. Wajnryb, P. Lang, Y.-N. Young, J.K.G. Dhont, B. Cichocki We present theoretical, numerical, and experimental investigations of evane\-scent-wave dynamic light scattering (EWDLS) in a wall-bounded colloidal suspension of spheres. The first cummulant $\Gamma_1$ representing the initial decay of the time autocorrelation function of the scattered field is expressed in terms of the hydrodynamic tensor $\mathbf{H}_w(\kappa,\mathbf{q})$ describing response of the suspension to a spatially varying harmonic force damped exponentially away from the wall. The wavelength of the harmonic spatial variation corresponds to the scattering vector $\mathbf{q}$ in the EWDLS experiments, and the exponential decay is characterized by the decay length $\kappa^{-1}$ of the evanescent wave. The hydrodynamic tensor $\mathbf{H}_w$ is evaluated using viral expansion at low densities and numerical simulations at higher densities. A complex non-isotropic structure of the tensor $\mathbf{H}_w(\kappa,\mathbf{q})$ reflects the hydrodynamic particle-wall coupling and wall-induced short range suspension ordering. Our theory and simulations agree well with the results of EWDLS experiments. [Preview Abstract] |
Monday, November 23, 2009 3:48PM - 4:01PM |
LT.00002: A 3-D Multiphase Particle Lattice Boltzmann Model of Colloidal Drop Dynamics Abhijit Joshi, Ying Sun A three-dimensional lattice Boltzmann method (LBM) has been developed for multiphase flows with particle suspensions. The unique challenge of this approach is to simulate the dynamics of liquid, vapor, and suspended particles in a stable manner. Adhesive forces between the suspended particles and the surrounding fluids are added to the previous single-phase particle suspension models and inter-particle forces are also taken into account. The model is first used to study the dynamics of colloidal drop coalescence for different particle sizes and concentrations. Results show that the liquid-vapor interface corresponds to a local energy minimum for the suspended particles. The wetting, dewetting, contact line pinning, and particle self-assembly of a colloidal drop is then examined as the drop spreads and evaporates on patterned (hydrophobic and hydrophilic) substrates. Evaporation is modeled using a quasi-static mass removal process. The drop wetting kinetics and final particle deposition are studied as a function of the surface energy step and pattern width of the substrate, as well as the particle size and volume fraction. Results are compared with experimental observations. [Preview Abstract] |
Monday, November 23, 2009 4:01PM - 4:14PM |
LT.00003: Hydrodynamic interactions between two semi-flexible in-extensible filaments in Stokes flow Yuan-Nan Young Hydrodynamic interactions between two semi-flexible in-extensible filaments are shown to have a significant impact on filament buckling and their subsequent motion in Stokesian fluids. In linear shear flow, hydrodynamic interactions lead to filament shear dispersion that depends on the filament aspect ratio and the initial filament separation. In linear extensional flow, hydrodynamic interactions lead to complex filament dynamics around the stagnation point. These results suggest that hydrodynamic interactions need to be taken into account to determine the self-diffusion of non-Brownian semi-flexible filaments in a cellular flow [Phys. Rev. Lett., 99, 058303, 2007]. [Preview Abstract] |
Monday, November 23, 2009 4:14PM - 4:27PM |
LT.00004: Field activated alignment and bifurcations in rigid rod suspensions Arvind Gopinath, Sarah Bates, Anette Hosoi Weak fields tend to align hard rod suspensions and trigger bifurcations from steady to periodic states. Three canonical problems are studied to thresh out common dynamical characteristics - the effect of weak shear, intrinsic aligning capabilities due to paramagnetic effects and externally imposed alignment via active orienting motors that adhere to the rods. The focus is on the relationships between new bifurcating solutions and the symmetries broken in the process of emergence. Imposition of weakly non-equilibrium shear flow can result in global bifurcations that are not discernable by a linear stability analysis while destabilization due to effects of polarity are seen to yield local bifurcations. Our exact results are corroborated by detailed asymptotic studies and extend previously obtained results. [Preview Abstract] |
Monday, November 23, 2009 4:27PM - 4:40PM |
LT.00005: Numerical study of nonlinear interactions in suspensions of ideally polarizable spheres under electrophoresis Jae Sung Park, David Saintillan We investigate the dynamics in a suspension of interacting ideally polarizable spheres undergoing electrophoresis using theory and numerical simulations. In addition to the classical linear electrophoretic motion of the particles, it is shown that two types of nonlinear electrokinetic phenomena may also occur and result in relative motions. First, when several particles are present and field gradients are created, nonzero dielectrophoretic forces (DEP) may arise due to Maxwell stresses in the fluid. In addition, if the particles can polarize under the action of the applied field, induced-charge electrophoresis (ICEP) occurs and may induce relative motions through hydrodynamic interactions. These two nonlinear effects are first analyzed in the prototypical case of two equal-sized spheres using asymptotic methods and are predicted to result in particle pairings. Based on this analysis, numerical simulations of full-scale particle suspensions undergoing DEP and ICEP with periodic boundary conditions are also performed using a fast Smooth Particle-Mesh Ewald (SPME) algorithm. The simulations confirm that pairing dynamics occur, and results are presented on the suspension microstructure, velocity statistics and particle hydrodynamic diffusion. [Preview Abstract] |
Monday, November 23, 2009 4:40PM - 4:53PM |
LT.00006: The Polarization of Nanorods Submerged in an Electrolyte Solution and Subjected to an AC Electric Field Hui Zhao, Haim Bau Recently, there has been a growing interest in utilizing electric fields to position and separate rod-shaped particles such as DNA molecules, actin filaments, and nanorods. The polarization of the electric double layer enveloping the rod plays a critical role in determining the magnitude and direction of the rod's dipole moment. We calculate the dipole moment as a function of the electric field frequency, the rod's aspect ratio (length/radius), the rod's free surface charge, and the double layer's thickness. To this end, we solve the Poisson-Nernst-Planck equations for the ions' migration, diffusion, and convection. When the surface charge is small and the rod is short, the dipole moment is negative. As the rod's length increases, the dipole moment increases, and eventually changes sign from negative to positive. The dipole coefficient of rods, whose length is greater than some critical value, increases linearly with length. The theoretical predictions are compared and favorably agree with experimental data for short DNA molecules. [Preview Abstract] |
Monday, November 23, 2009 4:53PM - 5:06PM |
LT.00007: The Role of Particle Deformation in the Rheology and Microstructure of Noncolloidal Suspensions Jonathan Clausen, Daniel Reasor, Cyrus Aidun Particle deformation creates a marked effect on the rheology of noncolloidal suspensions. More pronounced non-Newtonian behavior such as shear-thinning and normal stress differences can be seen as compared with rigid particle suspensions. In this study, a lattice-Boltzmann-method fluid is coupled to a finite-element-method solid to simulate three-dimensional deformable particles. A Lees--Edwards boundary condition is implemented in the lattice-Boltzmann method, which allows the investigation of bulk suspension properties. Simulation results focus on shear viscosity and normal stress differences, as well as microstructure parameters such as the Taylor deformation index. Simulations of hundreds of three-dimensional deformable particles are presented in unbounded shear at concentrations up to 40\%. Results include suspensions of solid elastic spheres, spherical capsules with elastic membranes, and model red blood cells. [Preview Abstract] |
Monday, November 23, 2009 5:06PM - 5:19PM |
LT.00008: The Role of Deformation in the Rheology and Orientaiton of Noncolloidal Fiber Suspension Cyrus Aidun, Jingshu Wu The microstructure and rheology of noncolloidal fibers suspended in Newtonian fluid are investigated with direct numerical simulation based on the external boundary force lattice-Boltzmann method. In this method, the flow is computed on a fixed regular ``lattice'', where each solid particle, or fiber in this case, is mapped onto a Lagrangian frame moving continuously through the domain. The motion and orientation of the fiber are obtained from Newtonian dynamics equations. The fiber bending ratio (BR) has significant influence on the flow rheology in the range BR $<$ 3, where for BR $>$ 3, the fiber can be considered as rigid. We show that in fiber suspension under shear, the relative viscosity decreases significantly as BR increases in the range of volume fraction from 1.7 to 12.4 percent considered in this study. This variation in relative viscosity appears to be well-correlated with the mean ``contact'' number. The effect of BR on the relative viscosity can also be explained based on the fiber orientation distribution. For increasing BR (more rigid fiber), the orientation distribution becomes narrower showing fibers oriented in the vicinity of the shear plane for a longer time, thus reducing the suspension shear viscosity. A small asymmetry of the fiber distribution is observed in the small BR regime, indicating the importance of fiber--fiber interaction and fiber deformation at BR$<$3. [Preview Abstract] |
Monday, November 23, 2009 5:19PM - 5:32PM |
LT.00009: Rheology of a suspension of non-linear elastic particles in a viscous shear flow Howard Hu, Tong Gao, Pedro Ponte Castaneda The rheology of a suspension of two-dimensional (2D) non-linear elastic particles in a Newtonian viscous shear flow is studied. The particles are assumed to be neutrally buoyant and composed of neo-Hookean material.The deformation of the particle is governed by the Reynolds number ($Re$) and the Capillary number ($Ca$). In the Stokes flow regime, the particle deforms into a steady elliptic shape while material points inside experiencer a tank-treading like motion. In the dilute limit, a perturbation analysis is performed for a slightly deformed particle in a infinite media to calculate the effective properties of the mixture. 2D Einstein viscosity for rigid particle is recovered at the leading order. For particles with large deformation, the effective stress components and viscosity are calculated by assist of a numerical simulation. A monolithic finite element solver which uses Arbitrary Lagrangian-Eulerian moving mesh technique is implemented to solve the velocity, pressure and stress in both fluid and solid phase simultaneously. The results are also compared with previous works on linear elastic or viscoelastic particles in a viscous liquid. [Preview Abstract] |
Monday, November 23, 2009 5:32PM - 5:45PM |
LT.00010: ABSTRACT HAS BEEN MOVED TO PE.00009 |
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