硬球加强模型在CFD-DEM耦合计算中的验证与分析

Verification and analysis of hard ball reinforced model in CFD-DEM coupling calculation

针对CFD-DEM耦合计算中,颗粒计算时间步的选取影响颗粒碰撞计算精度和效率的问题。本文引入插值算法,将动量定理求解颗粒碰撞前后速度进行加权平均;根据弹性理论计算得到颗粒碰撞力,进行动力学方程求解;通过速度收敛准则修正初值速度并自动调整迭代求解次数,提出一种计算精度不受计算时间步长影响,无需对碰撞过程进行精细描述的高效率和高精度的加强硬球模型。对两个颗粒匀和变速碰撞算例进行数值模拟,碰撞后速度、碰撞力和碰撞时间与理论计算误差小于4%,与采用软球碰撞模型的DEM方法相比,颗粒碰撞计算精度不受计算时间步长影响,计算效率提高36.3%和36.8%。对单个颗粒在静水中沉降进行数值模拟,计算步长取10 s~5 s,颗粒与壁面即可得到精确解,计算效率提高33.5%。通过压力损失实验验证了该模型能够准确计算颗粒体积分数小于12%条件下两相流的压力损失。

In the CFD-DEM coupling calculation,the choice of particle calculation time step affects the accuracy and efficiency of particle collision calculation.This paper introduces an interpolation algorithm to calculate the particle collision force before and after the weighted average by means of the momentum theorem;calculate the particle collision force according to the elastic theory,and solve the dynamic equation;use the velocity convergence criterion to correct the initial value of the velocity and automatically adjust the number of iterations.A high-efficiency and high-precision reinforced hard-ball model that is not affected by the calculation time step and does not require a detailed description of the collision process is proposed.Numerical simulation of two particle in uniform and variable-speed collision cases shows that the errors of the post-collision velocity,collision force,collision time are less than 4%,compared with those from the DEM method using the soft ball collision model,the particle collision calculation accuracy is not affected by the calculation time step,and the calculation efficiency is increased by 36.3%and 36.8%,respectively.The numerical simulation of the settlement of a single particle in still water is carried out,and the calculation step is 10 s~5 s.The particle and the wall can be accurately solved,and the calculation efficiency is increased by 33.5%.The pressure loss experiment verifies that the model can accurately calculate the pressure loss of two-phase flow when the particle volume fraction is less than 12%.