Lattice Boltzmann simulations of incompressible liquid-gas systems on partial wetting surfaces

A three-dimensional Lattice Boltzmann two-phase model capable of dealing with large liquid and gas density ratios and with a partial wetting surface is introduced. This is based on a high density ratio model combined with a partial wetting boundary method. The predicted three-dimensional droplets at different partial wetting conditions at equilibrium are in good agreement with analytical solutions. Despite the large density ratio, the spurious velocity around the interface is not substantial, and is rather insensitive to the examined liquid and gas density and viscosity ratios. The influence of the gravitational force on the droplet shape is also examined through the variations of the Bond number, where the droplet shape migrates from spherical to flattened interface in tandem with the increase of the Bond number. The predicted interfaces under constant Bond number are also validated against measurements with good agreements.     

Lattice Boltzmann simulations of bubble formation in a microfluidic T-junction

A lattice Boltzmann equation method based on the Cahn-Hilliard diffuse interface theory is developed to investigate the bubble formation process in a microchannel with T-junction mixing geometry. The bubble formation process has different regimes, namely, squeezing, dripping and jetting regimes, which correspond to the primary forces acting on the system. Transition from regime to regime is generally dictated by the capillary number Ca, volumetric flow ratio Q and viscosity ratio λ. A systematic analysis is performed to evaluate these effects. The computations are performed in the range of 10(-4)相似文献   

Lattice Boltzmann simulations of binary fluid flow through porous media

The lattice Boltzmann equation is often advocated as a simulation tool that is particularly effective for complex fluids such as multiphase and multicomponent flows through porous media. We construct a three-dimensional 19 velocity lattice Boltzmann model for immiscible binary fluids with variable viscosities and density ratio based on the model proposed by Gunstensen. The model is tested for the following binary fluid flow problems: a stationary planar interface among two fluids; channel flow of immiscible binary fluids; the Laplace problem; and a rising bubble. The results agree well with semi-analytic results in a range of the E?tv?s, Morton and Reynolds number. We also present preliminary simulation results for two large-scale realistic applications: the flow of an air-water mixture in a waste-water batch reactor and the saturation hysteresis effect in soil flow. We discuss some limitations of the lattice Boltzmann method in the simulation of realistic and difficult multiphase problems.     

A dynamic mesh refinement technique for Lattice Boltzmann simulations on octree-like grids

In this contribution, we present our new adaptive Lattice Boltzmann implementation within the Peano framework, with special focus on nanoscale particle transport problems. With the continuum hypothesis not holding anymore on these small scales, new physical effects—such as Brownian fluctuations—need to be incorporated. We explain the overall layout of the application, including memory layout and access, and shortly review the adaptive algorithm. The scheme is validated by different benchmark computations in two and three dimensions. An extension to dynamically changing grids and a spatially adaptive approach to fluctuating hydrodynamics, allowing for the thermalisation of the fluid in particular regions of interest, is proposed. Both dynamic adaptivity and adaptive fluctuating hydrodynamics are validated separately in simulations of particle transport problems. The application of this scheme to an oscillating particle in a nanopore illustrates the importance of Brownian fluctuations in such setups.     

Isochoric specific heat in the methane-ethane system around the liquid-gas critical line

Experimental and theoretical studies have been made on the behavior of the isochoric specific heat for binary methane-ethane mixtures in the critical region.     

Lattice Boltzmann simulation of flow past a non-spherical particle

Lattice Boltzmann method was used to predict the fluid-particle interaction for arbitrary shaped particles. In order to validate the reliability of the present approach, simulation of flow past a single stationary spherical, cylindrical or cubic particle is conducted in a wide range of Reynolds number (0.1 < Re_p < 3000). The results indicate that the drag coefficient is closely related to the particle shape, especially at high Reynolds numbers. The voxel resolution of spherical particle plays a key role in accurately predicting the drag coefficient at high Reynolds numbers. For non-spherical particles, the drag coefficient is more influenced by the particle morphology at moderate or high Reynolds numbers than at low ones. The inclination angle has an important impact on the pressure drag force due to the change of projected area. The simulated drag coefficient agrees well with the experimental data or empirical correlation for both spherical and non-spherical particles.     

微通道气体流动的格子波尔兹曼模拟

通过隐式格子波尔兹曼方程,并采用壁面平衡边界条件以及二阶关系,模拟了微通道气体流动中的非线性压力和壁面滑移速度,模拟结果与Arkilic的解析结果十分吻合,验证了格子波尔兹曼方法在滑移流区的有效性.     

Lattice Boltzmann method study of Rayleigh instability of a charged droplet

Rayleigh instability of a charged droplet is well known. Although the instability condition was revealed by Lord Rayleigh, how the deformation develops after the unstable state still remains a question because of its dynamic nature. Therefore, a numerical simulation method will help to study the dynamics of the deformation of a charged droplet. In this paper we reported an interesting extension of the multi-phase lattice Boltzmann method to involve the electrostatic repulsive force working on the surface of an individual liquid droplet by means of momentum modification to simulate the Rayleigh instability. The method successfully simulates the Rayleigh instability, in which a droplet is stretched into an ellipsoidal shape when the electrostatic potential exceeds the Rayleigh's threshold, whilst a droplet with less potential than the threshold deforms back to a spherical shape as the static form.     

Modeling of Metal Foaming with Lattice Boltzmann Automata

The formation and decay of foams produced by gas bubble expansion in a molten metal is numerically simulated with the Lattice Boltzmann Method (LBM) which belongs to the cellular automaton techniques. The present state of the two dimensional model allows the investigation of the foam evolution process comprising bubble expansion, bubble coalescence, drainage, and eventually foam collapse. Examples demonstrate the influence of the surface tension, viscosity and gravity on the foaming process and the resulting cell structure. In addition, the potential of the LBM to solve problems with complex boundary conditions is illustrated by means of a foam developing within the constraints of a mould as well as a foaming droplet exposed to gravity.     

Numerical simulation of microparticles transport in a concentric annulus by Lattice Boltzmann Method

Dispersion and removal of microaerosol particles are investigated numerically in a horizontal concentric annulus by Lattice Boltzmann Method and Lagrangian Runge–Kutta procedure with the assumption of one-way coupling. Drag, buoyancy, gravity, shear lift, Brownian motion and thermophoretic are forces that are included in particle equation of motion. All simulations were performed at Rayleigh number of 10⁴ and particles specific density of 1000. The effect of aspect ratio and particles diameter were determined on particles behavior such as removal and dispersion. Results show that recirculation power increases by decreasing of cylinders gap. Particles move in a thinner quasi-equilibrium region by increasing of their diameter and decreasing of cylinders gap. Brownian motion is dominant removal mechanism in particle with diameter of 1 μm.     

Hybrid Lattice Boltzmann Equation Method in Problems of Coupled Heat Transfer

Journal of Engineering Physics and Thermophysics - A hybrid (LB–FD) mathematical model has been constructed to investigate thermogravitational convection in closed rectangular cavities...     

Lattice gas simulations of dynamical geometry in one dimension

We present numerical results obtained using a lattice gas model with dynamical geometry. The (irreversible) macroscopic behaviour of the geometry (size) of the lattice is discussed in terms of a simple scaling theory and obtained numerically. The emergence of irreversible behaviour from the reversible microscopic lattice gas rules is discussed in terms of the constraint that the macroscopic evolution be reproducible. The average size of the lattice exhibits power-law growth with exponent at late times. The deviation of the macroscopic behaviour from reproducibility for particular initial conditions ('rogue states') is investigated as a function of system size. The number of such 'rogue states' is observed to decrease with increasing system size. Two mean-field analyses of the macroscopic behaviour are also presented.     

泥石流的增强碰撞算子格子Boltzmann模型

利用增强碰撞算子格子的Boltzmann方法,分析泥石流作为非Newton体的特点,根据泥石流的Bingham体模型,构造了一个特殊的增强碰撞算子的格子Boltzmann模型,并由此成功地模拟了泥石流入汇主河的运动过程,为预测和防治泥石流入汇主河所造成的灾害提供了一些理论依据。     

Lattice Boltzmann simulation of dispersion in two‐dimensional tidal flows

A lattice Boltzmann method (LBM) is applied to problems of dispersion in two‐dimensional water flows. The water flow is modelled by shallow water equations. A two‐distribution lattice Boltzmann equation algorithm is presented to solve the pollutant transport problem within the framework of shallow water flow. One distribution models the shallow water flow. The other distribution models the pollutant transport. Flow characteristics and concentration profiles of dispersive species are obtained at various flow regimes. For fast water flow, the concentration profiles are highly affected by the flow advection and become completely different from those at slow water flow. Numerical results are presented for pollutant transport in bounded and open channel flows. The proposed LBM is also used to simulate a pollution event in the Strait of Gibraltar. The obtained results indicate that the present method is useful for the investigation of transport phenomena by shallow water flows in complex geometries and practical flow problems. Copyright © 2008 John Wiley & Sons, Ltd.     

Parallel Implementation of the Hybrid Lattice Boltzmann Method on Graphics Accelerators

Journal of Engineering Physics and Thermophysics - An analysis has been conducted for the computational performance of a hybrid mathematical model for investigating the laws of thermogravitational...     

瓶体内表面制备类金刚石膜流场结构的格子波尔兹曼模拟

类金刚石膜(Diamond-like Carbon,DLC)具有优异的气体阻隔性能.在PET瓶体内表面制备DLC阻隔涂层时,阻隔涂层的均匀性会受到瓶体内流场结构(气压分布、速度分布等)的显著影响.本文应用格子波耳兹曼方法(Lattice Boltzmann Method/Model,LBM)对PET瓶体内制备DLC阻隔涂层时的流场结构进行模拟,研究了送气速度、气体运动粘度系数和装置结构变化时瓶体内部流场结构的变化.研究结果表明,降低进气速度和提高气体运动粘度系数有利于减弱回流而获得层流结构;装置结构的调整能够改变瓶体内的流场结构,采用恰当的异型装置可以获得较理想的流场结构,对实验工作具有一定的指导意义.     

Direct simulations of the linear elastic displacements field based on a lattice Boltzmann model

In this paper, a lattice Boltzmann model for simulating linear elastic Lame equation is proposed. Differently from the classic lattice Boltzmann models, this lattice Boltzmann model is based on displacement distribution function in lattice Boltzmann equation. By using the technique of the higher‐order moments of equilibrium distribution functions and a series of partial differential equations in different time scales, we obtain the Lame equation with fourth‐order truncation errors. Based on this model, some problems with small deflection are simulated. The comparisons between the numerical results and the analytical solutions are given in detail. The numerical examples show that the lattice Boltzmann model can be used to solve problems of the linear elastic displacement field with small deflection. Copyright © 2015 John Wiley & Sons, Ltd.     

Molecular dynamics simulations of motion of edge and screw dislocations in a metal

Motions of a straight edge dislocation and a kinked screw dislocation in BCC Mo, described by the Finnis–Sinclair potential, are studied in periodic simulation cells subjected to an applied shear stress. Procedures for setting up the initial atomic configurations in each case are described, and estimate is made of the local driving force due to the image interactions. Preliminary results show that at low temperature the edge dislocation moves primarily through kink nucleation, whereas the mobility of the screw dislocation is strongly facilitated by the presence of a kink.