垂直管内固-液两相流全耦合CFD-DEM模型研究

针对传统两相流CFD-DEM模型中忽略一些次要力以及颗粒-湍流作用导致计算精度不高的问题,建立了考虑Loth升力、虚拟质量力、压力梯度力以及湍流调制等多种机制的全耦合模型,分析了进口颗粒体积分数、输送速度和颗粒直径对固-液两相流动的影响。研究结果表明,升力驱使颗粒向管道中心聚集,且Loth升力比传统Saffman和Magnus升力预测的颗粒分布更接近实验。随着进口颗粒体积分数的增加,各相的轴向速度均明显减小,同时颗粒对湍流的调制作用导致流体均方根速度降低。随着输送速度的增加,颗粒在管道中心更加聚集,而流体均方根速度快速增加。随着颗粒直径的增加,颗粒在管道中的分布更加不均匀,而对流体均方根速度的影响很小。输送速度对压降影响最大,进口颗粒体积分数次之,颗粒直径对其影响最小。

Solid-liquid Two-phase Flow Based on Fully Coupled CFD-DEM Method in Vertical Pipe

Traditional CFD-DEM model for solid-liquid two-phase flow usually ignored some minor forces and complex particle-turbulence interaction, which led to the insufficient computational accuracy and failure to capture certain important phenomena. A fully coupled CFD-DEM model considering the Loth lift force, virtual mass force, pressure gradient force and turbulence modulation was established to overcome these problems for solid liquid two-phase flow. This fully coupled CFD-DEM model well predicted the particle distribution, two-phase velocity and turbulent kinetic energy in the pipe and can be used for the numerical study of solid-liquid two-phase flow. This model was used to analyze the effects of particle volume fraction at the pipe inlet, conveying speed and particle diameter on the characteristics of solid-liquid two-phase flow in the vertical pipe. The results showed that the lift force drove the particles towards the center of the pipe, and the distribution of particles predicted by the Loth lift force was more consistent with the experiment than that of the traditional Saffman and Magnus lift force. With the increase of the particle volume fraction at the pipe inlet, the axial velocity of each phase was decreased obviously in the pipe, and the effect of turbulence modulation from particles on turbulence led to the decrease of the fluid root mean square (RMS) velocity. With the increase of conveying speed, particles gathered more in the center of the pipe, and the RMS velocity of the fluid was increased rapidly. With the increase of particle diameter, the distribution of particles in the pipe was more uneven, but the effect on the RMS velocity of fluid was very small. The pressure drop was increased gradually with the increase of the particle volume fraction at the pipe inlet, and increased sharply with the increase of conveying speed. Coarse particle diameter had little effect on the pressure drop.