基于CFD-DEM耦合并行算法的锥形喷动床内离散颗粒数值模拟

Numerical simulation of discrete particles in conical-base spouted bed based on parallel coupled CFD-DEM model

基于FLUENT软件的MPI平台,在二次开发框架内通过用户自定义函数文件实现了CFD-DEM耦合并行算法.该并行算法具有随CPU核数增加的较佳扩展性能和良好加速性能.通过构建空隙率标量场、重组基于局部平均并考虑气-固相互作用的气相控制方程,提高了气相控制方程的求解稳定性与收敛性;通过软球模型确定颗粒-颗粒及颗粒-壁面间的相互作用,以曳力模型为基础建立了相间相互作用关系.将该CFD-DEM耦合并行模型应用于锥形喷动床气固两相流动的数值模拟中,结果表明:该CFD-DEM耦合并行模型能较好地模拟锥形喷动床内气固流动行为;锥形喷动床内的颗粒流动经历了鼓泡阶段和稳定流态化阶段;在稳定流态化阶段,物料流动具有明显的周期性.基于锥形喷动床内颗粒相的瞬时速度场,获得了稳定流态化阶段颗粒的时均速度分布规律.

Based on MPI （Message Passing Interface）platform of FLUENT software,the parallel technique for coupled CFD （computational fluid dynamics）-DEM（discrete element method）model is implemented by user defined functions in the framework of secondary development,which has good scalability and acceleration performance with the increase of CPU number.The convergence of the governing equations is improved by constructing the void fraction scalar field and reorganizing the governing equations of the gas phase which follow the volume-averaged form of the two-fluid model.Inter-particle and particle-wall interactions are determined with the soft-sphere model and the two phases are coupled based on the drag model.The parallel coupled CFD-DEM model is applied to the simulation of gas-particle two-phase flow in a conical-base spouted bed.Simulation results show that this model could well simulate gas-flow behavior in the spouted bed.Two distinct regions can be identified：the start-up and stable fluidization stage.In the stable fluidization stage,an oscillation cycle period can be observed,and the characteristics of the time-averaged particle velocity are obtained on the basis of the instantaneous particle velocity field.