Automatic Evolutionary Modeling by the Lattice-Boltzmann Method

The Lattice-Boltzmann method is an effective tool for solving fluid mechanics problems, but there isn't still a good scheme to determinate some parameters in Boltzmann equations. In this paper, a technique using evolutionary algorithm to automatically model Boltzmann equations is introduced. Numerical simulation shows that the designed scheme is fast and efficient.

Simulation of Droplet Impact onto Horizontal and Inclined Solid Surfaces with Lattice-Boltzmann Method

In this paper, the lattice-Bohzmann method is used to investigate the droplet dynamics after impact on horizontal and inclined solid surface. The two-phase interparticle potential model is employed. The model is found to possess a linear relation between the macroscopic properties （ surface tension σ and contact angle α） and microscopic parameters （ G, G, ）. The flow state of the droplet on the surface is analyzed in detail, and the effects of surface characteristic, impact velocity, impact angle, the viscosity and surface tension of the liquid are investigated, respectively. It is shown that the lattice-Bohzmann method can not only track exactly and automatically the interface, but also the simulation results have a good qualitative agreement with ones of the previous experimental and numerical studies.

Simulation and Experimental Study on Thermal Conductivity of Nano-Granule Porous Material Based on Lattice-Boltzmann Method

Nano-porous materials have excellent thermal insulation performance,whose microstructure and physical properties,however,have great influence on the thermal conductivity.To accurately describe the stochastic phase distribution,a random internal morphology and structure generation-growth method,called the quartet structure generation set(QSGS),has been proposed in the present paper.The model was then imported into lattice Boltzmann algorithm as a fully resolved geometry and used to investigate the effects on heat transfer at the nanoscale.Furthermore,a three-dimensional Lattice Boltzmann method(LBM)D3Q15 was adopted to predict the nano-granule porous material effective thermal conductivity.This ideal method provided a significant advantage over similar porous media methods by directly controlling and adjusting of granule characteristics such as granule size,porosity and pore size distributions and studying their influence directly on thermal conductivity.To verify the accuracy of the proposed model,some experiments based on guarded hot plate meter(GHPM)were conducted.The results indicated that the simulation results agreed well with the experimental data and references values,which illustrated that this method was reliable to generate the microstructure of nano-granule.What’s more,the effects of pressure,core distribution probability,cd and density were investigated.There existed an optimal density(about 120 kg·m^(-3))making the effective thermal conductivity being minimum and an optimal core distribution probability about cd=0.1 making the uniformity being the best.In addition,the present approach is applicable in dealing with other porous materials as well.

Lattice-Boltzmann simulations for analysing the detachment of micron-sized spherical particles from surfaces with large-scale roughness structures

Fully resolved numerical simulations of a micron-sized spherical particle residing on a surface with large-scale roughness are performed by using the Lattice-Boltzmann method.The aim is to investigate the influence of surface roughness on the detachment of fine drug particles from larger carrier particles for transporting fine drug particles in a DPI(dry powder inhaler).Often the carrier surface is modified by mechanical treatments for modifying the surface roughness in order to reduce the adhesion force of drug particles.Therefore,drug particle removal from the carrier surface is equivalent to the detachment of a sphere from a rough plane surface.Here a sphere with a diameter of 5μm at a particle Reynolds number of 1.0,3.5 and 10 are considered.The surface roughness is described as regularly spaced semi-cylindrical asperities(with the axes oriented normal to the flow direction)on a smooth surface.The influence of asperity distance and size ratio(i.e.the radius of the semi-cylinder to the particle radius,Rc/Rd)on particle adhesion and detachment are studied.The asperity distance is varied in the range 1.2<L/Rd<2 and the semi-cylinder radius between 0.5<Rc/Rd<0.75.The required particle resolution and domain size are appropriately selected based on numerical studies,and a parametric analysis is performed to investigate the relationship between the contact distance(i.e.half the distance between the particle contact points on two neighbouring semi-cylinders),the asperity distance,the size ratio,and the height of the particle centroid from the plane wall.The drag,lift and torque acting on the spherical particle are measured for different particle Reynolds numbers,asperity distances and sizes or diameters.The detachment of particles from rough surfaces can occur through lift-off,sliding and rolling,and the corresponding detachment models are constructed for the case of rough surfaces.These studies will be the basis for developing Lagrangian detachment models that eventually should allow the optimisation of dry powder inhaler performance through computational fluid dynamics.

Unified stability condition for particulate and aggregative fluidization—Exploring energy dissipation with direct numerical simulation

Fully resolved simulations of particulate and aggregative fluidization systems are performed suc-cessfully with the so-called combined lattice Boltzmann method and time-driven hard-sphere model （LBM-TDHS）. In this method, the discrete particle phase is described by time-driven hard-sphere model, and the governing equations of the continuous fluid phase are solved with lattice Boltz-mann method. Particle-fluid coupling is implemented by immersed moving boundary method. Time averaged flow structure of the simulated results show the formation of core-annulus structure and sigmoid distribution of voidage in the axial direction, which are typical phenomena in fluidization systems. Combining the results of the simulation, the energy consumption Nst for suspending and transporting solids is calculated from the direct numerical simulation （DNS） of fluidization, and the stability criterion Nst/NT = rain proposed in EMMS/bubbling model is verified numerically. Further-more the numerical results show that the value of Nst/NT in particulate fiuidization is much higher than that in aggregative fluidization, but Nst/NT = rain is effective for both particulate and aggregative fluidization.

Determining the impact of rectangular grain aspect ratio on tortuosity–porosity correlations of two-dimensional stochastically generated porous media

Tortuosity is an important parameter for char- acterizing transport properties within porous materials and is of interest in a broad range of fields, such as energy storage and conversion materials. One of the parameters that impacts the tortuosity value is the geometry of the solid phase which, in this study, is considered as stochas- tically-placed rectangular particles. Through lattice Boltz- mann modelling （LBM）, we determined the impact of particle aspect ratio on the intrinsic tortuosity-porosity relationships of two-dimensional porous media composed of rectangular particles. These relationships were isolated for materials with grain （particle） aspect ratios of e { 1, 2, 3 } and porosities from [0.55 - 0.95]. We determined that a minimum of 6, 8 and 10 stochastic simulations, respec- tively, were required to calculate these average tortuosity values in laminar flow （Re 〈〈 1）. This novel application of the LBM to study the effects of porosity and aspect ratio of rectangular grains on tortuosity can be used in the tailoring of materials for clean energy.