气固两相流介尺度LBM-DEM模型

LBM-DEM耦合方法通常是指一种颗粒流体系统直接数值模拟算法,即是一种不引入经验曳力模型的计算方法,颗粒尺寸通常比计算网格的长度大一个量级,颗粒的受力通过表面的粘性力与压力积分获得,其优点是能描述每个颗粒周围的详细流场,产生详细的颗粒-流体相互作用的动力学信息,可以探索颗粒流体界面的流动、传递和反应的详细信息及两相相互作用的本构关系,但其缺点是计算量巨大,无法应用于真实流化床过程模拟。本文针对气固流化床中的流体以及固体颗粒间的多相流体力学行为,建立了一种稠密气固两相流的介尺度LBMDEM模型,即LBM-DEM耦合的离散颗粒模型,实现在颗粒尺度上流化床的快速离散模拟。该耦合模型采用格子玻尔兹曼方法(LBM)描述气相的流动和传递行为,离散单元法(DEM)用于描述颗粒相的运动,并利用能量最小多尺度(EMMS)曳力解决气固耦合不成熟问题,以提高其模拟精度。通过经典快速流态化的模拟,验证了介尺度LBM-DEM耦合模型的有效性。模拟结果表明介尺度LBM-DEM模型是一种探索实验室规模气固系统的有力手段。

Mesoscale LBM-DEM model for gas-solid two-phase flow

A coupled Lattice Boltzmann Method and Discrete Element Method (LBM-DEM) approach is usually a kind of Direct Numerical Simulation (DNS) algorithms for particle-fluid system,in which fluid-solid interactions are realized without any empirical drag correlation,the size of fluid grid is generally one magnitude smaller than particle diameter,and force acting on particles directly calculated by integrating both viscos force and pressure gradient force on the particle surface.The advantages of the method are that it is capable of exploring the flow,transport and reaction details at the gas-solid interface,and establishing the constitutive laws for the simulations at the scales above.However,it has the main disadvantage of huge computational cost,and it is still formidable to simulate the hydrodynamics of an industrial fluidized bed.This paper aims to investigate the hydrodynamic behaviors of multiphase flow between fluid and solid particles in gas-solid fluidized beds,establish a meso-scale LBM-DEM method for the dense gas-solid two-phase flow in which the size of fluid grid is one magnitude larger than particle diameter,and realize the fast discrete simulation of fluidized beds at particle scale.The proposed method describes the flow and transport behaviors by the LBM,tracks the motion of particles by the DEM,and utilizes the energy-minimization multi-scale (EMMS) drag for correcting the interaction between gas and solid particles to improve the simulation accuracy.Fast fluidization in a riser is successfully simulated and the results are in good agreement with experimental data.The numerical results show that the proposed method can be a powerful tool for exploring lab-scale gas-solid systems.