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Dispersion of charged tracers in charged porous media

EPL 2008年第3期83卷

作者： Rotenberg, B. Pagonabarraga, I. Frenkel, D. FOM Inst Atom & Mol Phys NL-1098 SJ Amsterdam Netherlands ANDRA F-92298 Chatenay Malabry France Univ Barcelona Dept Fis Fonamental E-08028 Barcelona Spain Univ Cambridge Dept Chem Cambridge CB2 1EW England

We report a lattice-Boltzmann scheme to compute the dispersion of charged tracers in charged porous media under the combined effect of advection, diffusion and electro-migration. To this end, we extend the moment propagation approach, introduced to study the dispersion of neutral tracers (Lowe C. and FRENKEL D., Phys. Rev. Lett., 77 (1996) 4552), to include the effect of electrostatic forces. This method allows us to compute the velocity autocorrelation function of the charged tracers with high accuracy. The algorithm is validated studying the dispersion coefficient in the case of electro-osmotic flow in a slit without added salt. We find excellent agreement between the numerical and analytical results. This method also provides the full time dependence of the diffusion coefficient, including for charged tracers. We illustrate on the slit case how D(t), which is measured by NMR to probe the geometry of porous media, reflects how the porosity explored by tracers depends on their charge. Copyright (C) EPLA, 2008.

关键词： computational methods in fluid dynamics Flows through porous media Microemulsions

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Galilean invariance of lattice Boltzmann models

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EPL 2008年第3期81卷

作者： Nie, X. B. Shan, X. Chen, H. Exa Corp Burlington MA 01803 USA

It is well known that the original lattice Boltzmann (LB) equation deviates from the Navier-Stokes equations due to an unphysical velocity-dependent viscosity. This unphysical dependence violates the Galilean invariance and limits the validation domain of the LB method to near incompressible flows. As previously shown, recovery of correct transport phenomena in kinetic equations depends on the higher hydrodynamic moments. In this letter, we give specific criteria for recovery of various transport coefficients. The Galilean invariance of a general class of LB models is demonstrated via numerical experiments. Copyright (C) EPLA, 2008.

关键词： computational methods in fluid dynamics Kinetic theory Compressible flows, shock waves

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Lattice Boltzmann method for inhomogeneous fluids

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EPL 2008年第3期81卷

作者： Melchionna, S. Marconi, U. Marini Bettolo Univ Rome Dipartimento Fis INFM SOFT I-00185 Rome Italy Ist Nazl Fis Mat I-00185 Rome Italy Univ Camerino Dipartimento Fis INFM SOFT I-62032 Camerino Italy Ist Nazl Fis Mat I-62032 Camerino Italy

We present a lattice-based numerical method to describe the non-equilibrium behavior of a simple fluid under non-uniform spatial conditions. The evolution equation for the one-particle phase-space distribution function is derived starting from a microscopic description of the system. It involves a series of approximations which are similar to those employed in theories of inhomogeneous fluids, such as the density functional theory. Among the merits of the present approach: the possibility to determine the equation of state of the model, the transport coefficients and to provide an efficient method of numerical solution under non-uniform conditions. The algorithm is tested in a particular non-equilibrium situation, namely the steady flow of a hardsphere fluid across a narrow slit. Pronounced non-hydrodynamic oscillations in the density and velocity profiles are found. Copyright (C) EPLA, 2008.

关键词： computational methods in fluid dynamics Micro- and nano- scale flow phenomena Structure of liquids

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Evidence of thin-film precursors formation in hydrokinetic and atomistic simulations of nano-channel capillary filling

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EPL 2008年第4期84卷

作者： Chibbaro, S. Biferale, L. Diotallevi, F. Succi, S. Binder, K. Dimitrov, D. Milchev, A. Girardo, S. Pisignano, D. Univ Roma Tor Vergata Dept Mech Engn I-00133 Rome Italy CNR Ist Applicaz Calcolo I-00161 Rome Italy Ist Nazl Fis Nucl I-00133 Rome Italy Johannes Gutenberg Univ Mainz Inst Phys D-55099 Mainz Germany Bulgarian Acad Sci Inst Chem Phys BU-1113 Sofia Bulgaria Univ Lecce CNR I-73100 Lecce Italy

We present hydrokinetic Lattice Boltzmann and Molecular dynamics simulations of capillary filling of highly wetting fluids in nano-channels, which provide clear evidence of the formation of thin precursor films, moving ahead of the main capillary front. The dynamics of the precursor films is found to obey a square-root law as the main capillary front, z(2)(t) infinity t, although with a larger prefactor, which we find to take the same value for both geometries under inspection. Both hydrokinetic and Molecular dynamics approaches indicate a precursor film thickness of the order of one tenth of the capillary diameter. The quantitative agreement between the hydrokinetic and atomistic methods indicates that the formation and propagation of thin precursors can be handled at a mesoscopic/hydrokinetic level, thereby opening the possibility of using hydrokinetic methods to space-time scales and complex geometries of direct experimental relevance. Copyright (C) EPLA, 2008

关键词： computational methods in fluid dynamics Liquid thin films Mehods of deposition of films and coatings, film growth and epitaxy

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Intriguing viscosity effects in confined suspensions: A numerical study

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EPL 2008年第6期83卷

作者： Davit, Y. Peyla, P. Univ Grenoble 1 Spectrometrie Phys Lab F-38402 St Martin Dheres France

The effective viscosity of dilute and semi-dilute suspensions in a shear flow in a microfluidic configuration is studied numerically. The suspension is composed of monodisperse and non-Brownian hard spherical buoyant particles confined between two walls in a shear flow. An abrupt change of the viscosity behaviour occurs with strong confinements: when the wall-to-wall distance is below five times the radius of the particles, we obtain a change of the sign of the contribution of the hydrodynamic interactions to the effective viscosity. This effect is the macroscopic counterpart of the peculiar micro-hydrodynamics of confined suspensions due to the influence of walls. In addition, for higher concentrations (above 25%), we find that the viscosity meets a minimum when the inter-wall distance is around five times the sphere radius. This phenomenon is reminiscent of the Fahraeus-Lindqvist effect for blood confined in small capillaries. However, we show that for sheared confined semi-dilute suspensions, the physical origin of this minimum is not due to a migration effect but to the change of hydrodynamic interactions. Copyright (c) EPLA, 2008

关键词： Suspensions Rheological aspects computational methods in fluid dynamics

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Lattice Boltzmann modelling Knudsen layer effect in non-equilibrium flows

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EPL 2008年第4期83卷

作者： Tang, G. H. Zhang, Y. H. Gu, X. J. Emerson, D. R. SERC Daresbury Lab Computat Sci & Engn Dept Warrington WA4 4AD Cheshire England Univ Strathclyde Dept Mech Engn Glasgow G1 1XJ Lanark Scotland

Due to its intrinsically kinetic nature, lattice Boltzmann (LB) approach to simulating non-equilibrium gas flows has recently attracted significant research interest. Compared with other kinetic methods, it can offer a significantly smaller computational cost. To capture the nonlinear high-order rarefaction phenomena in gas flows, a geometry-dependent gas local mean free path has been proposed to be implemented in our "high-order" LB model. A series of tests on rarefaction effects and the Knudsen layer interference have been carried out and the simulation results demonstrate our LB model's capability for highly non-equilibrium flows. Copyright (c) EPLA, 2008.

关键词： computational methods in statistical physics and nonlinear dynamics Rarefied gas dynamics computational methods in fluid dynamics

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Shape changes and motion of a vesicle in a fluid using a lattice Boltzmann model

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EPL 2008年第5期81卷

作者： Li, H. B. Yi, H. H. Shan, X. W. Fang, H. P. Chinese Acad Sci Shanghai Inst Appl Phys Shanghai 201800 Peoples R China Guilin Univ Elect Technol Dept Informat Mat Sci & Engn Guilin 541004 Peoples R China Chinese Acad Sci Grad Sch Beijing 100080 Peoples R China EXA Corp Burlington MA 01803 USA

To study erythrocyte deformation and movement in fluid. flows, the membrane bending rigidity and elastic modulus are incorporated with a lattice Boltzmann simulation. The stable static biconcave shape is found to resist pathological membrane changes, and the erythrocyte exhibits tank tread-like motion with a highly flattened shape in a shear flow. With intrinsically parallel dynamics, this lattice Boltzmann method may apply to both single and multi-vesicle suspension and complex open membranes in various. fluid. flows for a wide range of Reynolds numbers. Copyright (c) EPLA, 2008.

关键词： computational methods in fluid dynamics Disperse systems, complex fluids General theory in fluid dynamics

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Modeling of urban traffic networks with lattice Boltzmann model

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EPL 2008年第4期81卷

作者： Meng, Jian-Ping Qian, Yue-Hong Dai, Shi-Qiang Shanghai Univ Shanghai Inst Appl Math & Mech Shanghai 200072 Peoples R China Zhejiang Normal Univ Coll Math Phys & Informat Engn Jinhua 321004 Peoples R China

It is of great importance to uncover the characteristics of traffic networks. However, there have been few researches concerning kinetics models for urban traffic networks. In this work, a lattice Boltzmann model (LBM) for urban traffic networks is proposed by incorporating the ideas of the Biham-Middleton-Levine (BML) model into the LBM for road traffic. In the present model, situations at intersections with the red and green traffic signals are treated as a kind of boundary conditions varying with time. Thus, the urban traffic network could be described in the mesoscopic level. By performing numerical simulations under the periodic boundary conditions, the behavior of average velocity is investigated in detail. The numerical results agree quite well with those given by the Chowdhury-Schadschneider (ChSch) model (CHOWDHURY D. and SCHADSCHNEIDER A., Phys. Rev. E, 59 (1999) R1311). Furthermore, the statistical noise is reduced in this discrete kinetics model, thus, the present model has considerably high computational efficiency. Copyright (C) EPLA, 2008.

关键词： computational methods in fluid dynamics Kinetic theory Granular models of complex systems, traffic flow

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Lattice Boltzmann spray-like fluids

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EPL 2008年第2期82卷

作者： Falcucci, G. Chibbaro, S. Succi, S. Shan, X. Chen, H. Univ Roma Tre Dept Mech & Ind Engn Rome Italy CNR Ist Applicaz Calcolo Mauro Picone Rome Italy Univ Tor Vergata Dept Mech Engn Rome Italy EXA Corp Lexington MA 02173 USA

The effect of the competition between short-range attraction and mid-range repulsion in lattice Boltzmann models of single-component non-ideal fluids is investigated. It is shown that the presence of repulsive interactions gives rise to long-lived metastable states in the form of multi-droplet spray-like density configurations, whose size can be adjusted by fine-tuning the strength of the repulsive vs. attractive coupling. This opens up the possibility of using single-component lattice kinetic models to study a new class of complex flow applications, involving atomization, spray formation, micro-emulsions and possibly, glassy-like phenomena as well. Copyright (c) EPLA, 2008.

关键词： computational methods in fluid dynamics Gas/liquid flows Surfactant effects

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A bottom-up approach to non-ideal fluids in the lattice Boltzmann method

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EPL 2008年第6期81卷

作者： Zhang, Junfeng Tian, Fuzhi Laurentian Univ Sch Engn Sudbury ON P3E 2C6 Canada

The Shan-Chen ( SC) pseudopotential lattice Boltzmann model for multiphase fluids has been revised to incorporate the particle exclusion-volume effect. Previous attempts to simulate a non-ideal fluid with the SC model tailored the interparticle potential to obtain the desired equation of state. Such an approach lumped the contributions from the particle exclusion-volume effect and the interparticle interactions together, and undermined the excellent physical basis of the SC model. In this letter, the equilibrium distributions are modified to include the particle exclusion-volume effect, and the clear physical meaning of interparticle potential in the original SC model has been reserved. Without losing the simple mathematical formulation and unique physical representation, the revised model can easily model non-ideal fluids with various equations of state. A vander Waals fluid has also been simulated as an example to demonstrate the significance of this improvement. Copyright (c) EPLA, 2008.

关键词： Surface tension and related phenomena computational methods in fluid dynamics Thermodynamic functions and equations of state

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