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A reduced-order model for heat transfer in multiphase flow and practical aspects of the proper orthogonal decomposition

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COMPUTERS & CHEMICAL ENGINEERING 2012年 43卷 68-80页

作者： Brenner, Thomas A. Fontenot, Raymond L. Cizmas, Paul G. A. O'Brien, Thomas J. Breault, Ronald W. Texas A&M Univ Dept Aerosp Engn College Stn TX 77843 USA Dept Energy Natl Energy Technol Lab Morgantown WV 26507 USA

This paper discusses two practical aspects of reduced-order models (ROMs) based on proper orthogonal decomposition (POD) and presents the derivation and implementation of a ROM for non-isothermal multiphase flow. The POD method calculates basis functions for a reduced-order representation of two-phase flow by calculating the eigenvectors of an autocorrelation matrix composed of snapshots of the flow. The flow is divided into transient and quasi-steady regions and two methods are shown for clustering snapshots in the transient region. Both methods reduce error as compared to the constant sampling case. The ROM for non-isothermal flow was developed using numerical results from a full-order computational fluid dynamics model for a two-dimensional non-isothermal fluidized bed. Excellent agreement is shown between the reduced- and full-order models. The composition of the autocorrelation matrix is also considered for an isothermal case. An approach treating field variables separately is shown to produce less error than a coupled approach. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Proper orthogonal decomposition Reduced-order modeling Multiphase flow computational methods in fluid dynamics

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Flow simulations with multi-particle collision dynamics

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MECCANICA 2012年第8期47卷 2069-2077页

作者： De Angelis, E. Chinappi, M. Graziani, G. Univ Roma La Sapienza Dipartimento Ingn Meccan & Aerosp I-00184 Rome Italy Univ Bologna DIEM I-47100 Forli Italy Univ Roma La Sapienza Dipartimento Fis I-001185 Rome Italy

Multi-particle collision dynamics (MPCD) is a particle based Navier-Stokes solver and in the last ten years it has been largely used to analyze mesoscopic systems where both hydrodynamics and thermal effects have to be taken into account, typical examples being colloidal suspensions and polymer solutions. Though the soundness of this approach is well documented, only a few studies present a systematic validation of the method as a Navier-Stokes solver for relatively complex flows (e.g. unsteady, non-uniform). In this study we use MPCD to simulate an unsteady periodic flow (second Stokes' problem) and a two dimensional flow (lid-driven cavity). Quantitative comparisons with analytical and finite difference results show that MPCD is able to correctly reproduce the hydrodynamics of these systems in a wide range of numerical parameter values, allowing the applications of MPCD to the analysis of complex fluids in confined geometries such as in Lab-On-a-Chip microfluidic devices. Discrepancies for certain parameter ranges and in specific flow conditions are singled out and discussed.

关键词： computational methods in fluid dynamics Multi-particle collision dynamics

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Effects of force discretization on mass conservation in lattice Boltzmann equation for two-phase flows

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EPL 2012年第6期99卷

作者： Lou, Q. Guo, Z. L. Shi, B. C. Huazhong Univ Sci & Technol Natl Lab Coal Combust Wuhan 430074 Peoples R China Huazhong Univ Sci & Technol Sch Math & Stat Wuhan 430074 Peoples R China

Discretization of interaction force is an important issue in the lattice Boltzmann equation (LBE) method for two-phase systems. A variety of discretization schemes for the interaction force have been developed from different viewpoints. Although these schemes are totally identical mathematically, they may have quite different behaviors in actual applications. In this paper we investigate the mass conservation properties of four discretization forcing schemes that have been adopted in a variety of two-phase LBE models. It is found that LBE with the mixed scheme does not conserve the total mass, and the violation is related to grid resolution, fluid velocity, and density variation. Copyright (C) EPLA, 2012

关键词： General theory in fluid dynamics computational methods in fluid dynamics Multiphase and stratified flows

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Fluctuation-dissipation relation from a FLB-BGK model

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EPL 2012年第6期99卷

作者： Basagaoglu, H. Melchionna, S. Succi, S. Yakhot, V. SW Res Inst Geosci & Engn Div San Antonio TX 78238 USA Univ Roma La Sapienza Dept Phys Inst Proc Chim Fis Uos Roma IPCF CNR I-00185 Rome Italy CNR IAC I-00161 Rome Italy Boston Univ Dept Mech Engn Boston MA 02215 USA

A two-dimensional colloidal fluctuating lattice-Boltzmann (FLB-BGK) model was formulated by adopting the most popular version of the fluctuating lattice-Boltzmann algorithm in the literature and explicitly incorporating the finite size and shape of particles. In this formulation, random noise was added to the fluid to simulate thermal fluctuations of the fluid at mesoscopic length scales. The resulting random perturbations acting on the particle surface were responsible for particle Brownian motion. FLB-BGK simulations with a thermally perturbed fluid in a confined channel involving a Brownian particle near a channel wall displayed perfect equipartitioning and thermalization in the absence of any external force. The simulations captured a crossover from a ballistic regime to a diffusive regime at which particle velocity autocorrelation vanished. FLB-BGK simulations with an inert particle in thermally perturbed, creeping or low-medium Reynolds number flows in confined channels showed that particle motion obeyed the fluctuation-dissipation theorem if the wall effects on particle motion were absent or small. On the other hand, the fluctuation-dissipation theorem was found not to hold in the presence of significant wall effects on particle motion. Copyright (C) EPLA, 2012

关键词： Hydrodynamics, hydraulics, hydrostatics Low-Reynolds-number (creeping) flows computational methods in fluid dynamics

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Lattice Boltzmann model for reactive flow simulations

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EPL 2012年第3期98卷

作者： Di Rienzo, A. F. Asinari, P. Chiavazzo, E. Prasianakis, N. I. Mantzaras, J. Politecn Torino Dipartimento Energia I-10129 Turin Italy Paul Scherrer Inst Combust Res Lab CH-5232 Villigen Switzerland

In this letter, we propose a lattice Boltzmann (LB) model for reactive flow simulations at the low-Mach-number regime, which is suitable to accommodate significant density variation. A recently proposed model for compressible thermal flows on standard lattices is herein extended to combustion applications, where species equations are properly described in order to account for compressibility effects. This fundamental extension allows to apply LB approach to a wide range of combustion phenomena, which were not properly addressed so far. The effectiveness of the proposed approach is proved by simulating combustion of hydrogen/air mixtures in a mesoscale channel, and a validation against reference numerical solution in the continuum limit is presented. Copyright (C) EPLA, 2012

关键词： computational methods in fluid dynamics Reactive and radiative flows Kinetic theory

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Lattice Boltzmann study of thermal phase separation: Effects of heat conduction, viscosity and Prandtl number

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EPL 2012年第4期97卷

作者： Gan, Yanbiao Xu, Aiguo Zhang, Guangcai Zhang, Ping Li, Yingjun Inst Appl Phys & Computat Math Natl Key Lab Computat Phys Beijing 100088 Peoples R China N China Inst Aerosp Engn Langfang 065000 Peoples R China China Univ Min & Technol Beijing State Key Lab GeoMech & Deep Underground Engn SMCE Beijing 100083 Peoples R China

We investigate the effects of heat conduction, viscosity, and Prandtl number on thermal liquid-vapor separation via a lattice Boltzmann model for van der Waals fluids. The set of Minkowski measures on the density field enables to divide exactly the stages of the spinodal decomposition (SD) and domain growth. The duration t(SD) of the SD stage decreases with increasing the heat conductivity kappa(T) but increases with increasing the viscosity eta. The two relations can be fitted by t(SD) = a+ b/kappa(T) and t(SD) = c+ d eta +(e eta)(3), respectively, where a, b, c, d and e are fitting parameters. For fixed Prandtl number Pr, when eta is less than a critical value eta(c), t(SD) shows an inverse power-law relationship with eta. However, when eta > eta(c), t(SD) for Pr > 1 shows qualitatively different behavior. From the evolution of the Peclet number Pe, the separation procedure can also be divided into two stages. During the first stage, the convection effects become more dominant with time over those of the diffusivity, while they are reverse in the second stage. Copyright (C) EPLA, 2012

关键词： computational methods in fluid dynamics Morphological instability, phase changes Nonequilibrium and irreversible thermodynamics

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Electro-osmotic flows under nanoconfinement: A self-consistent approach

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EPL 2011年第4期95卷

作者： Melchionna, S. Marconi, U. Marini Bettolo Univ Roma La Sapienza CNR IPCF I-00185 Rome Italy Univ Camerino INFN Perugia Scuola Sci & Tecnol I-62032 Camerino Italy

We introduce a theoretical and numerical method to investigate the properties of electro-osmotic flows under conditions of extreme confinement. The present approach, aiming to provide a simple modeling of electrolyte solutions described as ternary mixtures, which comprises two ionic species and a third uncharged component, is an extension of our recent work on binary neutral mixtures. The approach, which combines elements of kinetic theory, density functional theory with Lattice-Boltzmann algorithms, is microscopic and self-consistent and does not require the use of constitutive equations to determine the fluxes. Numerical solutions are obtained by solving the resulting coupled equations for the one-particle phase-space distributions of the species by means of a Lattice-Boltzmann discretization procedure. Results are given for the microscopic density and velocity profiles and for the volumetric and charge flow. Copyright (C) EPLA, 2011

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

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A heuristic curved-boundary treatment in lattice Boltzmann method

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EPL 2010年第5期92卷

作者： Chen, Sheng Bao, Sheng Liu, Zhaohui Li, Jing Yi, Chao Zheng, Chuguang Huazhong Univ Sci & Technol State Key Lab Coal Combust Wuhan 430074 Peoples R China

Curved boundary treatments provide a way to improve the computational accuracy of the conventional stair-shaped approximation used in lattice Boltzmann (LB) simulations. However, the existing methods either require at least two or three fluid nodes between nearby solid surfaces, a condition that cannot be satisfied in the scenarios where only one fluid node is available, or break the mass conservation at the solid- wall surface that may result in serious numerical instability. Until now there is no boundary treatment that can remedy these two disadvantages with secondorder accuracy at the same time. In this letter, we develop a heuristic curved-boundary treatment for the LB method from the viewpoint of surface chemistry. This simple scheme can overcome the aforementioned disadvantages synchronously. The numerical experiments show that the present scheme gives second- order accuracy. Moreover, the midway bounce- back scheme and the nonequilibrium extrapolation scheme for boundary treatment both can be recovered from the present scheme. Copyright (C) EPLA, 2010

关键词： computational methods in fluid dynamics Interactions with surfaces Kinetic theory of gases

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Electromagnetic waves in lattice Boltzmann magnetohydrodynamics

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EPL 2010年第5期90卷

作者： Dellar, P. J. Math Inst OCIAM Oxford OX1 3LB England

An existing lattice Boltzmann formulation of non-relativistic magnetohydrodynamics represents the magnetic field using a set of vector-valued distribution functions. By expressing the behaviour of this system using a basis of moments of the distribution functions, we derive an evolution equation for the electric field that coincides with the combination of Maxwell's equation, including the displacement current, and Ohm's law. Numerical experiments verify the propagation of electromagnetic waves radiated from an oscillating dipolar current. Copyright (C) EPLA, 2010

关键词： Classical electromagnetism, Maxwell equations Electromagnetic wave propagation, radiowave propagation computational methods in fluid dynamics

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Polymer rheology simulations at the meso- and macroscopic scale

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EPL 2010年第6期90卷

作者： Sultan, E. de Meent, J. -W. van Somfai, E. Morozov, A. N. van Saarloos, W. Leiden Univ Inst Lorentz Theoret Phys NL-2300 RA Leiden Netherlands Univ Paris Sud UPMC Univ Paris 06 CNRS UMR 7608 F-91405 Orsay France Univ Warwick Dept Phys Coventry CV4 7AL W Midlands England Univ Warwick Ctr Complex Sci Coventry CV4 7AL W Midlands England Univ Edinburgh JCMB Sch Phys Edinburgh EH9 3JZ Midlothian Scotland

We show that simulations of polymer rheology at a fluctuating mesoscopic scale and at the macroscopic scale where flow instabilities occur can be achieved at the same time with dissipative particle dynamics (DPD) technique. We model the viscoelasticity of polymer liquids by introducing a finite fraction of dumbbells in the standard DPD fluid. The stretching and tumbling statistics of these dumbbells is in agreement with what is known for isolated polymers in shear flows. At the same time, the model exhibits behaviour reminiscent of drag reduction in the turbulent state: as the polymer fraction increases, the onset of turbulence in plane Couette flow is pushed to higher Reynolds numbers. The method opens up the possibility to model non-trivial rheological conditions with ensuing coarse-grained polymer statistics. Copyright (c) EPLA, 2010

关键词： Polymers and polymer solutions Viscoelasticity, plasticity, viscoplasticity computational methods in fluid dynamics

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