A Numerical Simulation of the Boycott Effect

The lattice Boltzmann method has been used to simulate the velocity field induced and the motion of an ensemble of particles during the sedimentation process in inclined tubes. The simulations show the trajectories and flow behavior of individual particles and particle-particle and particle-wall interactions as well as the formation of particle clusters. The global convection motion that was experimentally observed during such processes and tends to enhance the sedimentation process is also reproduced numerically. In addition we have found that smaller intermittent vortices, formed from the wakes of groups of settling particles, also play an important role in the sedimentation process and the final distribution of particles.     

Numerical model for the computation of permeability of a cemented granular material

We present a 3D model designed to compute permeability in a cemented polydisperse granular material composed of spherical grains. A non-cohesive granular deposit is constructed by means of the Discrete Element Method (DEM) then cement is deposited on grains using three simple models. Finally the solid sample is subjected to an upward hydraulic gradient in order to measure permeability. The fluid flow through the connected sample pores is modeled using the Lattice Boltzmann Method (LBM). The computed permeability coefficients are in good agreement with the existing classical values. The evolution of permeability with the cement deposit growth is studied for the three proposed cementation models.     

旋流除沙器流体旋转效果的数值模拟

介绍了一种新型的旋流除沙器,并利用FLUENT软件对旋流除砂器内流体的流动旋转情况进行了数值模拟。根据数值模拟的结果,分析、预测了旋流除沙器内流体的旋转情况,并分析了模拟结果产生的原因,对后续的模拟研究进行了讨论。     

管道泄漏污染物一维迁移的LBM模拟

石油管道泄漏现象时有发生,对环境造成了危害,研究埋地管道石油污染物泄漏尤为关键。在此采用Boltzmann研究方法,通过多尺度技术和局部平衡态分布函数的Chapman-Enskog展开得到运算的平衡态方程,并给出了石油管道污染物泄漏迁移的一维有源扩散方程的格子Boltzmann模型,通过C++软件数值模拟进行运算。最终得出结果与理论解一致,验证了用Boltzmann方法研究污染物泄漏迁移的可行性。     

节流间隙宽度对直通式迷宫密封泄漏量的影响

应用格子Boltzmann方法计算直通式迷宫密封中不同间隙宽度对迷宫密封流场和泄漏的影响。计算结果与分析表明,不同间隙宽度对密封不可压缩流体流场和泄漏量有一定的影响,随着间隙宽度的增加,泄漏量增大,在保证安全的情况下应尽量减小间隙宽度。     

Numerical simulation of natural convection in a square enclosure filled with nanofluid using the two-phase Lattice Boltzmann method

Considering interaction forces (gravity and buoyancy force, drag force, interaction potential force, and Brownian force) between nanoparticles and a base fluid, a two-phase Lattice Boltzmann model for natural convection of nanofluid is developed in this work. It is applied to investigate the natural convection in a square enclosure (the left wall is kept at a high constant temperature (T_H), and the top wall is kept at a low constant temperature (T_C)) filled with Al₂O₃/H₂O nanofluid. This model is validated by comparing numerical results with published results, and a satisfactory agreement is shown between them. The effects of different nanoparticle fractions and Rayleigh numbers on natural convection heat transfer of nanofluid are investigated. It is found that the average Nusselt number of the enclosure increases with increasing nanoparticle volume fraction and increases more rapidly at a high Rayleigh number. Also, the effects of forces on nanoparticle volume fraction distribution in the square enclosure are studied in this paper. It is found that the driving force of the temperature difference has the biggest effect on nanoparticle volume fraction distribution. In addition, the effects of interaction forces on flow and heat transfer are investigated. It is found that Brownian force, interaction potential force, and gravity-buoyancy force have positive effects on the enhancement of natural convective heat transfer, while drag force has a negative effect.     

Simulation of packed bed reactors using lattice Boltzmann methods

Lattice Boltzmann (LB) methods are used to simulate hydrodynamics, reaction and subsequent mass transfer in a disordered packed bed of catalyst particles at sub-pore length-scales. In contrast to previous studies, a variety of modifications are introduced in the LB method enabling particle Pe numbers up to 10⁸, and hence realistic values of diffusivity, to be accessed. These include decoupling the hydrodynamics from mass transfer and the use of a rest fraction in the LB formulation of mass transfer. In addition the mass transfer simulations are modified to permit spatially varying values of diffusivity, essential to differentiate between intra- and inter-particle diffusivity (D_intra and D_inter, respectively). The simulation method is applied to both a disordered and ordered 2D packing for a range of Pe (15.6-1557.8) and Re (0.16-1.56) numbers, as well as various ratios of D_intra/D_inter (0-1), whilst simulating an esterfication reaction catalyzed by an ion-exchange resin. The value of D_intra is found to have limited effect, whilst reducing Pe number results in a considerable increase in overall conversion. The simulation method is then applied to a 3D lattice for which experimental conversion data is available. This experimental data is straddled by the simulation case of D_intra=0 and D_intra=D_inter, as expected.     

Simulation of forced convection in a channel with nanofluid by the lattice Boltzmann method

This paper presents a numerical study of the thermal performance of fins mounted on the bottom wall of a horizontal channel and cooled with either pure water or an Al₂O₃-water nanofluid. The bottom wall of the channel is heated at a constant temperature and cooled by mixed convection of laminar flow at a relatively low temperature. The results of the numerical simulation indicate that the heat transfer rate of fins is significantly affected by the Reynolds number (Re) and the thermal conductivity of the fins. The influence of the solid volume fraction on the increase of heat transfer is more noticeable at higher values of the Re.     

Numerical Simulation for Particle Penetration Depth Distribution in Deep Bed Filtration

A two‐dimensional model has been developed to simulate particle penetration through porous media. The particle penetration depends on many parameters including the Reynolds number, particle drag coefficient, the ratio of the diameter of injected to filtered particles, fluid velocity, and pore size, etc. The numerical model for separation efficiency in periodic porous media was studied. Previous work has described the effects of injected particle size, Reynolds number and particle drag coefficient. In this study, the porous media flow is modeled (solution of the Navier‐Stokes equations) by using the finite element method, and the analysis is restricted to the case of two‐dimensional periodic porous media. The effects of these factors and particle depth distribution in porous media are investigated. It is noted that the results for the three Reynolds numbers 1, 16.56, and 100, are qualitatively similar, and about 40 % of particles are trapped in the top part of the filter.     

Simulation of 3D velocity and concentration profiles in a packed bed adsorber by lattice Boltzmann methods

Full 3D simulations of velocity and concentration profiles were carried out for the several ordered packing arrangements of spherical particles with small tube-to-particle diameter ratio (<10) using lattice Boltzmann methods. The effects of voids and diffusion coefficients on the adsorption concentration profiles in a packed bed of circular cross-section were investigated. In particular, the radial (r) and circumferential (θ) dependencies of the concentrations due to non-uniform velocity and particle voids across tube's cross-section, especially near the walls, were ascertained. The lattice Boltzmann technique allows simultaneous solution to velocity and concentration fields at all locations inside the packed tube without using any empirical correlations for certain transport parameters, for example, dispersion coefficient. Depending upon the packing arrangements and the magnitudes of diffusion coefficient, the concentration gradients in r- and θ-directions were found to be significant. The lattice model simulation results were also compared to the tomographic data obtained in a tubular adsorber packed with the zeolites coated glass beads and were found to be in reasonably good agreement.     

Numerical study and acceleration of LBM-RANS simulation of turbulent flow

The coupled models of LBM(Lattice Boltzmann Method) and RANS(Reynolds-Averaged Navier–Stokes) are more practical for the transient simulation of mixing processes at large spatial and temporal scales such as crude oil mixing in large-diameter storage tanks. To keep the efficiency of parallel computation of LBM, the RANS model should also be explicitly solved; whereas to keep the numerical stability the implicit method should be better for RANS model. This article explores the numerical stability of explicit methods in 2D cases on one hand, and on the other hand how to accelerate the computation of the coupled model of LBM and an implicitly solved RANS model in 3D cases. To ensure the numerical stability and meanwhile avoid the use of empirical artificial limitations on turbulent quantities in 2D cases, we investigated the impacts of collision models in LBM(LBGK, MRT)and the numerical schemes for convection terms(WENO, TVD) and production terms(FDM, NEQM) in an explicitly solved standard k–ε model. The combination of MRT and TVD or MRT and NEQM can be screened out for the 2D simulation of backward-facing step flow even at Re = 10~7. This scheme combination, however, may still not guarantee the numerical stability in 3D cases and hence much finer grids are required, which is not suitable for the simulation of industrial-scale processes. Then we proposed a new method to accelerate the coupled model of LBM with RANS(implicitly solved). When implemented on multiple GPUs, this new method can achieve 13.5-fold acceleration relative to the original coupled model and 40-fold acceleration compared to the traditional CFD simulation based on Finite Volume(FV) method accelerated by multiple CPUs. This study provides the basis for the transient flow simulation of larger spatial and temporal scales in industrial applications with LBM–RANS methods.     

Effect of surface property on mass flux in a variable-section microchannel

For microfluidic systems, interfacial phenomena in micro-reactors are of great importance because they control the transfer and reaction characteristics. This paper dwells on how the surface property and geometry influence the mass flux in a complex microchannel. The lattice Boltzmann method(LBM) with a pseudo potential model and the Shan–Chen model for the interaction between fluid and hydrophobic surface were built up, so a boundary slip effect was added and verified. On this basis, a microchannel with variable-section geometry was simulated. The results indicate that the optimal design and the flow pattern are quite different under hydrophilic and hydrophobic conditions. A microchannel with sequential hydrophilic and hydrophobic surface was also simulated. The numerical results indicate that the hydrophobic wall can improve the mass flux, irrespective of microchannel geometry. Particularly, an empirical correlation with a linearly relationship between length of hydrophobic segment and mass flux was obtained for the straight microchannel.     

Numerical simulation of the flow field in the mixing section of a screw extruder by the lattice Boltzmann model

The single-screw extruder is commonly used in polymer processing where the performance of the mixing section is significant in determining the quality of the final product. It is therefore of great interest to simulate the flow field in a single-screw extruder. In this paper the simulation is performed using the lattice Botlzmann model giving a fast and efficient numerical technique. The solution is compared to a finite difference and lattice gas simulation and found to give more accurate results.     

Interaction of two touching spheres in a viscous fluid

The nature and effects of contacts between suspended particles were studied through a process in which a heavy sphere falls past a light sphere in a viscous fluid at low Reynolds number. Teflon and nylon spheres were used for the heavy and light spheres, respectively, with natural surface roughness and with the nylon sphere artificially roughened. Because of the existence of microscopic roughness on the sphere surfaces, the particles are able to make physical contact, breaking the symmetry of the trajectory predicted by hydrodynamic theory for smooth spheres. The experimental results are compared with numerical results calculated according to the theory of Davis (Phys. Fluids A 4 (1992) 2607), with a particular focus on the rotational velocities of the spheres. The numerical results from the roll/slip model provide the best fit of the experimental data. Instead of locking together like a rigid body and rotating together, two spheres initially roll without slipping and then roll with slipping after the maximum friction force is reached.     

固体炸药冲击起爆尺寸效应的数值模拟

固体炸药样品的装药尺寸对其冲击起爆的特性有着比较明显的影响，本文利用非线性有限元方法模拟计算了JO－9159炸药冲击起爆过程，分析了炸药冲击起爆过程的尺寸效应，结果表明，在一定范围内，JO－9159炸药的起爆力阈值随装直径和装药长度的增大而减小。     

Simulation of micro- and macro-transport in a packed bed of porous adsorbents by lattice Boltzmann methods

In this study we report 3D simulation of concentration profiles in a fixed bed packed with spherical porous adsorbents using lattice Boltzmann methods (LBMs). The lattice models have been developed to investigate evolution of concentration profiles due to inter- and intra-particle mass transport in an adsorber having small tube-to-sphere diameter (d_t/d_p) ratios. The multi-scaling feature of LBMs permits full 3D simulation of concentration profiles both in the bed voids and within the pores of the adsorbents without using any empirical correlations or without making 1D or 2D approximations that are usually made in traditional numerical methods. The model simulation is carried out for varying packing arrangements and small to large pore diffusivities. The simulation results show significant concentration gradients for small pore diffusivities and large particle size, which must be considered in predicting breakthrough and adsorption times for a tubular adsorber having d_t/d_p<10. The model predicted breakthrough curves are validated with the experimental data obtained by tomography technique in a tubular adsorber packed with zeolite particles.     

Numerical Investigation of Flow Patterns and Concentration Profiles in Y‐Mixers

The fluid flow patterns and associated concentration fields in Y‐mixers are investigated using lattice Boltzmann method‐based models. The focus lies on the impact of the mixing angle on the flow and concentration fields, with the mixing angle varying between acute (θ = 10°) and obtuse (θ = 130°) angles. Residence time distributions are determined to study the effect of the angles on the mixing and velocity patterns, in particular, different flow regimes, i.e., stratified laminar, vortex, and engulfment flow. The results from the simulations are validated with literature data and found to be in good agreement. Maximum mixing occurs in the 100° obtuse‐angle Y‐mixer, attributed to the extensive engulfment of flows in the mixing channel.     

基于格子Boltzmann方法的地下矿巷道系统突水与蔓延数字模拟

采用格子Boltzmann方法建立了巷道突水蔓延二维仿真模型.将物理巷道划分为网格模型,确定每个网格节点的基本物理量,对水粒子在网格模型内碰撞和迁移过程做了定义,巷道边界使用修正反弹格式,针对复杂巷道,使用分块耦合算法,将巷道分块处理,各块只在边界处进行数据交换,实现了不同块之间流场的耦合,简化计算,提高了程序效率.仿...