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Hydrodynamics of binary-fluid mixtures -An augmented Multiparticle Collison dynamics approach

EPL 2018年第2期121卷

作者： Eisenstecken, Thomas Hornung, Raphael Winkler, Roland G. Gompper, Gerhard Forschungszentrum Julich Inst Adv Simulat Theoret Soft Matter & Biophys D-52425 Julich Germany Forschungszentrum Julich Inst Complex Syst D-52425 Julich Germany

The Multiparticle Collision dynamics technique (MPC) for hydrodynamics simulations is generalized to binary-fluid mixtures and multiphase flows, by coupling the particle-based fluid dynamics to a Ginzburg-Landau free-energy functional for phase-separating binary fluids. To describe fluids with a non-ideal equation of state, an additional density-dependent term is introduced. The new approach is verified by applying it to thermodynamics near the critical demixing point, and interface fluctuations of droplets. The interfacial tension obtained from the analysis of the capillary-wave spectrum agrees well with the results based on the Laplace-Young equation. Phase separation dynamics follows the Lifshitz-Slyozov law. Copyright (C) EPLA, 2018

关键词： computational methods in fluid dynamics Computer simulation of molecular and particle dynamics Phase transitions: general studies

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Entropic multi-relaxation free-energy lattice Boltzmann model for two-phase flows

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EPL 2018年第1期122卷

作者： Bosch, F. Dorschner, B. Karlin, I. Swiss Fed Inst Technol Aerothermochem & Combust Syst Lab Inst Energy Technol Dept Mech & Proc Engn CH-8092 Zurich Switzerland

The entropic multi-relaxation lattice Boltzmann method is extended to two-phase systems following the free-energy approach. Gain in stability is achieved by incorporating the force term due to Korteweg's stress into the redefined entropic stabilizer, which allows simulation of higher Weber and Reynolds numbers with an efficient and explicit algorithm. Results for head-on droplet collisions and droplet impact on super-hydrophobic substrates are matching experimental data accurately. Furthermore, it is demonstrated that the entropic stabilization leads to smaller spurious currents without affecting the interface thickness. The present findings demonstrate the universality of the simple and explicit entropic lattice Boltzmann models and provide a viable and robust alternative to existing methods. Copyright (C) EPLA, 2018

关键词： computational methods in fluid dynamics Statistical mechanics of classical fluids Drops and bubbles

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Coupled RapidCell and lattice Boltzmann models to simulate hydrodynamics of bacterial transport in response to chemoattractant gradients in confined domains

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MICROfluidICS AND NANOfluidICS 2016年第2期20卷 1-14页

作者： Hoa Nguyen Basagaoglu, Hakan McKay, Cameron Carpenter, Alexander J. Succi, Sauro Healy, Frank Trinity Univ Dept Math San Antonio TX 78212 USA SW Res Inst Mech Engn Div San Antonio TX 78238 USA Inst Applicaz Calcolo CNR IAC Viale Policlin 137 I-00161 Rome Italy Trinity Univ Dept Biol San Antonio TX 78212 USA

The RapidCell (RC) model was originally developed to simulate flagellar bacterial chemotaxis in environments with spatiotemporally varying chemoattractant gradients. RC is best suited for motility simulations in unbounded nonfluid environments;this limits its use in biomedical applications hinging on bacteria-fluid dynamics in microchannels. In this study, we eliminated this constraint by coupling the RC model with the colloidal lattice Boltzmann (LB) model. RC-LB coupling was accomplished by tracking positions of chemoreceptors on particle surfaces that vary with particles' angular and translational velocities, and by including forces and torques due to particles' tumbling and running motions in particle force-and torque-balance equations. The coupled model successfully simulated trajectories of particles in initially stagnant fluids in bounded domains, involving a chemoattractant contained in a confined zone with a narrow inlet or concentric multiringed inline obstacles, mimicking tumor vasculature geometry. Chemotactically successful particles exhibited higher attractant concentrations near the receptor clusters, transient increases in the motor bias, and transient fluctuations in methylated proteins at the cell scale, while exhibiting more frequent higher particle translation velocities and smaller angular velocities than chemotactically unsuccessful particles at the particle scale. In these simulations, the chemotactic particles reached the chemoattractant with the success rates of 20-72 %, whereas nonchemotactic particles would be unsuccessful. The coupled RC-LB model is the first step toward development of a multiscale simulation tool that bridges cell-scale signal and adaptation dynamics with particle-scale fluid-particle dynamics to simulate chemotaxis-driven bacterial motility in microchannel networks, typically observed in tumor vasculatures, in the context of targeted drug delivery.

关键词： computational methods in fluid dynamics Hydrodynamics hydrostatics Chemotaxis

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Central-moments-based lattice Boltzmann schemes with force-enriched equilibria

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EPL 2017年第3期117卷

作者： De Rosis, Alessandro Technion Israel Inst Technol Dept Biomed Engn IL-32000 Haifa Israel Univ Lyon Ecole Cent Lyon CNRS Lab Mecan Fluides & Acoust F-69134 Ecully France

This paper presents a numerical scheme to account for external forces in the central-moments-based lattice Boltzmann method. Instead of deriving additional forcing operators, here we propose to incorporate forces directly in the equilibrium populations. The resultant concise methodology is validated against established well-defined problems admitting analytical solution, showing very good accuracy and convergence rate. Moreover, it outperforms the classical BGK kernel in terms of stability. Copyright (C) EPLA, 2017

关键词： Lattice gas computational methods in fluid dynamics Kinetic theory

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Non-orthogonal central moments relaxing to a discrete equilibrium: A D2Q9 lattice Boltzmann model

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EPL 2016年第4期116卷

作者： De Rosis, Alessandro Technion Israel Inst Technol Dept Biomed Engn IL-32000 Haifa Israel Univ Lyon CNRS Lab Mecan Fluides & Acoust Ecole Cent Lyon F-69134 Ecully France

A novel D2Q9 lattice Boltzmann scheme based on the relaxation of central moments is presented. Differently from previous efforts, here we introduce a non-orthogonal basis of moments which relax to a discrete local equilibrium. Under these choices, our proposed model recovers exactly the BGK collision kernel if a unique relaxation rate is adopted. Numerical tests involving well-consolidated canonical problems highlight the excellent properties of the algorithm in terms of accuracy, convergence and stability. Moreover, our formulation shows an intelligible derivation and a simple practical implementation. Copyright (C) EPLA, 2016

关键词： Lattice gas computational methods in fluid dynamics Kinetic theory

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Extended friction elucidates the breakdown of fast water transport in graphene oxide membranes

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EPL 2016年第5期116卷

作者： Montessori, A. Amadei, C. A. Falcucci, G. Sega, M. Vecitis, C. D. Succi, S. Univ Rome Roma Tre Dept Engn Via Vasca Navale 79 I-00141 Rome Italy Harvard Univ John A Paulson Sch Engn & Appl Sci Cambridge MA 02138 USA Univ Roma Tor Vergata Dept Enterprise Engn Mario Lucertini Via Politecn 1 I-00133 Rome Italy CNR Ist Applicaz Calcolo Via Taurini 19 I-00185 Rome Italy Univ Vienna Inst Computat Phys Sensengasse 8-9 A-1090 Vienna Austria

The understanding of water transport in graphene oxide (GO) membranes stands out as a major theoretical problem in graphene research. Notwithstanding the intense efforts devoted to the subject in the recent years, a consolidated picture of water transport in GO membranes is yet to emerge. By performing mesoscale simulations of water transport in ultrathin GO membranes, we show that even small amounts of oxygen functionalities can lead to a dramatic drop of the GO permeability, in line with experimental findings. The coexistence of bulk viscous dissipation and spatially extended molecular friction results in a major decrease of both slip and bulk flow, thereby suppressing the fast water transport regime observed in pristine graphene nanochannels. Inspection of the flow structure reveals an inverted curvature in the near-wall region, which connects smoothly with a parabolic profile in the bulk region. Such inverted curvature is a distinctive signature of the coexistence between single-particle zero-temperature (noiseless) Langevin friction and collective hydrodynamics. The present mesoscopic model with spatially extended friction may offer a computationally efficient tool for future simulations of water transport in nanomaterials. Copyright (C) EPLA, 2016

关键词： Micro- and nano- scale flow phenomena computational methods in fluid dynamics Graphene

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fluidisation and plastic activity in a model soft-glassy material flowing in micro-channels with rough walls

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EPL 2016年第6期114卷

作者： Scagliarini, A. Lulli, M. Sbragaglia, M. Bernaschi, M. Forschungszentrum Julich Helmholtz Inst Erlangen Nurnberg Renewable Energy Further Str 248 D-90429 Nurnberg Germany Univ Tor Vergata Dept Phys Via Ric Sci 1 I-00133 Rome Italy Univ Tor Vergata INFN Via Ric Sci 1 I-00133 Rome Italy Ist Applicazioni Calcolo CNR Via Taurini 9 I-00185 Rome Italy

By means of mesoscopic numerical simulations of a model soft-glassy material, we investigate the role of boundary roughness on the flow behaviour of the material, probing the bulk/wall and global/local rheologies. We show that the roughness reduces the wall slip induced by wettability properties and acts as a source of fluidisation for the material. A direct inspection of the plastic events suggests that their rate of occurrence grows with the fluidity field, reconciling our simulations with kinetic elasto-plastic descriptions of jammed materials. Notwithstanding, we observe qualitative and quantitative differences in the scaling, depending on the distance from the rough wall and on the imposed shear. The impact of roughness on the orientational statistics is also studied. Copyright (C) EPLA, 2016

关键词： computational methods in fluid dynamics computational techniques, simulations Complex fluids and colloidal systems

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Lattice Boltzmann simulations of vortex entrapment of particles in a microchannel with curved or flat edges

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MICROfluidICS AND NANOfluidICS 2015年第5-6期18卷 1165-1175页

作者： Basagaoglu, Hakan Carrola, John T., Jr. Freitas, Christopher J. Basagaoglu, Berkay Succi, Sauro SW Res Inst Mech Engn Div San Antonio TX 78238 USA SW Res Inst Div Appl Phys San Antonio TX 78238 USA Texas A&M Univ Dept Biomed Engn College Stn TX 77843 USA Ist Applicaz Calcolo I-00185 Rome Italy Harvard Univ IACS SEAS Cambridge MA 02138 USA

Numerical simulations were conducted to determine the effects of flat-edge and curved-edge channel wall obstacles on the vortex entrapment of uniform-size particles in a microchannel with a T-shape divergent flow zone at different flow Reynolds numbers (Re). Two-particle simulations with a non-pulsating flow indicated that although particles were consistently entrapped in a vortex zone in a microchannel with flat-edge wall obstacles at all Re studied, vortex zone entrapment of particles occurred only at the lowest Re in a microchannel with curved-edge wall obstacles. In a microchannel with flat-edge obstacles, small particles avoided entrapment in vortices in a non-pulsating flow where large particles got trapped. Interparticle and particle-wall repulsive interaction potentials prevented vortex entrapment of particles in a microchannel with flat-edge wall obstacles only at high flow Re, revealing the existence of a threshold inertial force for particle liberation, if combined inertial and repulsive forces are considered in non-pulsating flow simulations. Pulsating flow enhanced the chance for liberation of particles that were otherwise trapped in vortices, but did not always ensure the particle liberation. Simulations with larger particle concentrations demonstrated that the location of particle-trapping vortices varied with changes in particle concentration. Simulation results further demonstrated the significance of particle retaining capabilities of vortices in a T-shape divergent zone within a microchannel.

关键词： computational methods in fluid dynamics Hydrodynamics Vortex entrapment

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Slowing-down of non-equilibrium concentration fluctuations in confinement

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EPL 2015年第6期111卷

作者： Giraudet, Cedric Bataller, Henri Sun, Yifei Donev, Aleksandar Ortiz de Zarate, Jose Maria Croccolo, Fabrizio Univ Pau & Pays Adour Lab Fluides Complexes & Leurs Reservoirs F-64600 Anglet France NYU Courant Inst Math Sci New York NY 10012 USA Univ Complutense Dept Fis Aplicada 1 E-28040 Madrid Spain

Fluctuations in a fluid are strongly affected by the presence of a macroscopic gradient making them long- ranged and enhancing their amplitude. While small-scale fluctuations exhibit diffusive lifetimes, moderate-scale fluctuations live shorter because of gravity. In this letter we explore fluctuations of even larger size, comparable to the extent of the system in the direction of the gradient, and find experimental evidence of a dramatic slowing-down of their dynamics. We recover diffusive behavior for these strongly confined fluctuations, but with a diffusion coefficient that depends on the solutal Rayleigh number. Results from dynamic shadowgraph experiments are complemented by theoretical calculations and numerical simulations based on fluctuating hydrodynamics, and excellent agreement is found. Hence, the study of the dynamics of non-equilibrium fluctuations allows to probe and measure the competition of physical processes such as diffusion, buoyancy and confinement, i.e. the ingredients included in the Rayleigh number, which is the control parameter of our system. Copyright (C) EPLA, 2015

关键词： Nonequilibrium and irreversible thermodynamics Image forming and processing computational methods in fluid dynamics

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Novel risk predictor for thrombus deposition in abdominal aortic aneurysms

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EPL 2015年第2期112卷

作者： Nestola, M. G. C. Gizzi, A. Cherubini, C. Filippi, S. Succi, S. Univ Campus Biomed Rome Dept Engn I-00128 Rome Italy Univ Svizzera Italiana Fac Informat CH-6904 Lugano Switzerland ICRANet Int Ctr Relativist Astrophys Network Pescara Italy CNR Mauro Picone Inst I-00185 Rome Italy Harvard Univ Sch Engn & Appl Sci IACS Cambridge MA 02138 USA

The identification of the basic mechanisms responsible for cardiovascular diseases stands as one of the most challenging problems in modern medical research including various mechanisms which encompass a broad spectrum of space and time scales. Major implications for clinical practice and pre-emptive medicine rely on the onset and development of intraluminal thrombus in which effective clinical therapies require synthetic risk predictors/indicators capable of informing real-time decision-making protocols. In the present contribution, two novel hemodynamics synthetic indicators, based on a three-band decomposition (TBD) of the shear stress signal, are introduced. Extensive fluid-structure computer simulations of patient-specific scenarios confirm the enhanced risk-prediction capabilities of the TBD indicators. In particular, they permit a quantitative and accurate localization of the most likely thrombus deposition in realistic aortic geometries, where previous indicators would predict healthy operation. The proposed methodology is also shown to provide additional information and discrimination criteria on other factors of major clinical relevance, such as the size of the aneurysm. Copyright (C) EPLA, 2015

关键词： Hemodynamics computational methods in fluid dynamics Numerical approximation and analysis

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