Particle-Particle算法并行化及改进

介绍了particle-particle算法的基本原理,并对串行particle-particle算法进行有效的 并行化;对并行算法的受力计算和通信过程进行改进;最后给出了实验结果,并进行相关性 能分析．

Multi-fluid Eulerian simulation of mixing of binary particles in a gas-solid fluidized bed with a cohesive particle-particle drag model

A particle-particle(p-p)drag model is extended to cohesive particle flow by introducing solid surface energy to characterize cohesive collision energy loss.The effects of the proportion of cohesive particles on the mixing of binary particles were numerically investigated with the use of a Eulerian multiphase flow model incorporating the p-p drag model.The bed expansion,mixing,and segregation of Geldart-A and C particles were simulated with varying superficial velocities and Geldart-C particle proportions,from which we found that the p-p drag model can reasonably predict bed expansion of binary particles.Two segregation types of jetsam-mixture-flotsam and mixture-flotsam processes were observed during the fluidization processes for the Geldart-A and C binary particle system.The mixing processes of the binary particle system can be divided into three scales:macro-scale mixing,meso-scale mixing,and micro-scale mixing.At a constant superficial velocity the optimal mixing was observed for a certain cohesive particle proportion.

Numerical simulation of particle sedimentation in 3D rectangular channel

The 3D lattice Boltzmann method is used to simulate particle sedimentation in a rectangular channel.The results of single particle sedimentation indicate that the last position of the particle is along the center line of the channel regardless of the initial position,the particle diameter,and the particle Reynolds number.The wall effect on the terminal velocity is in good agreement with experimental results quantitatively.The drafting,kissing,and tumbling （DKT） process is reproduced and analyzed by simulating two-particle cluster sedimentation.The effects of the diameter ratio,initial position,and wall on the DKT process are investigated.When the two particles have equal diameter sediment in the rectangular channel,a periodical DKT process and the spiraling trajectory are found.The last equilibrium configuration is obtained from the simulation results.The interesting regular sedimentation phenomena are found when 49 particles fall down under gravity.

Differentially weighted direct simulation Monte Carlo method for particle collision in gas-solid flows

In gas-solid flows, particle-particle interaction （typical, particle collision） is highly significant, despite the small particles fractional volume. Widely distributed polydisperse particle population is a typical characteristic during dynamic evolution of particles （e.g., agglomeration and fragmentation） in spite of their initial monodisperse particle distribution. The conventional direct simulation Monte Carlo （DSMC） method for particle collision tracks equally weighted simulation particles, which results in high statistical noise for particle fields if there are insufficient simulation particles in less-populated regions. In this study, a new differentially weighted DSMC （DW-DSMC） method for collisions of particles with different number weight is proposed within the framework of the general Eulerian-Lagrangian models for hydrodynamics. Three schemes （mass, momentum and energy conservation） were developed to restore the numbers of simulation particle while keeping total mass, momentum or energy of the whole system unchanged respectively. A limiting case of high-inertia particle flow was numerically simulated to validate the DW-DSMC method in terms of computational precision and efficiency. The momentum conservation scheme which leads to little fluctuation around the mass and energy of the whole system performed best. Improved resolution in particle fields and dynamic behavior could be attained simultaneously using DW-DSMC, compared with the equally weighted DSMC. Meanwhile, computational cost can be largely reduced in contrast with direct numerical simulation.

Numerical analysis of frictional behavior of dense gas-solid systems

Dense gas-solid flows show significantly higher stresses compared with dilute flows, mainly attributable to particle-particle friction in dense particle flows. Several models developed have considered particle-particle friction; however, they generally underestimate its effect in dense regions of the gas-solid system, leading to unrealistic predictions in their flow patterns. Recently, several attempts have been made to formulate such flows and the impact of particle-particle friction on predicting flow patterns based on modified frictional viscosity models by including effects of bulk density changes on frictional pressure of the solid phase. The solid-wall boundary is also expected to have considerable effect on friction because particulate phases generally slip over the solid surface that directly affects particle-particle frictional forces. Polydispersity of the solid phase also leads to higher friction between particles as more particles have sustained contact in polydispersed systems. Their effects were investi- gated by performing CFD simulations of particle settlement to calculate the slope angle of resting material of non-cohesive particles as they settle on a solid surface. This slope angle is directly affected by frictional forces and may be a reasonably good measure of frictional forces between particles. The calculated slope angle, as a measure of frictional forces inside the system are compared with experimental values of this slope angle as well as simulation results from the literature.