水力旋流器内非牛顿流体多相流场的数值模拟

摘要

利用一种非牛顿流体黏度修正模型描述水力旋流器内高浓度矿浆的非牛顿流动特性,并结合雷诺应力模型(RSM)、混合多相流模型(Mixture)以及拉格朗日颗粒追踪模型(LPT)建立了一种适用于模拟水力旋流器内非牛顿流体多相流场的数学模型.模拟结果与报道的实验值的相对误差均在10％以内,表明了该模型的可靠性.结果表明,非牛顿流体黏度的空间分布与矿浆密度的空间分布类似.沿零轴速包络面(LZVV)的轮廓存在一个高密度环,其原因为某粒径范围内的颗粒受到的径向合力为零,颗粒群沿LZVV做高速旋转运动.分散相的空间分布取决于不同粒径的颗粒受力.对于不同粒径的单位质量颗粒,同外离心力的数值大约为向内压力梯度力的两倍左右,使得大颗粒进入下行流并在底流口收集.随着颗粒粒径的减小,总体向内且具有波动性的流体曳力呈指数增长.向内的流体曳力将部分颗粒推向轴心,经上行流逃逸,同时也增强了颗粒运动的随机性.当颗粒粒径小于一定值后,流体曳力远远大于离心力和压力梯度力,颗粒运动的随机性非常强,宏观表现为均匀分布.%The flow behavior of dense non-Newtonian slurry in a hydrocyclone was described by a viscosity correction model. Combined with the Reynolds stress model, the mixture multiphase model and the stochastic Lagrangian particle tracking model, a comprehensive computational fluid dynamics model was established to simulate the multiphase non-Newtonian flow in a hydrocyclone. The validity of the proposed model was verified by the reasonably good agreement between measured and predicted results with the deviation less than 10%. The results showed that the spatial distribution of slurry viscosity was similar to that of slurry density. The particles at a specific size range with zero radial resultant forces had high-speed rotational movement around the locus of zero vertical velocity (LZVV), resulting in a high density ring in the body. The spatial distribution of dispersed phase depended on the forces applied. For the particles of various sizes, the magnitude of outward centrifugal force was twice that of inward pressure gradient force. The large particles would enter the downward flow and be collected at the underflow. As particle size decreased, the overall inward drag force with varying direction increased exponentially. As a result, some relatively fine particles were pushed towards the air core and escaped from the overflow with the upward flow. Meanwhile, the randomness of such particle movement was enhanced. When particle size was below a critical value, which meant that the fluid drag force on the particles was much larger than centrifugal force and pressure gradient force, the randomness of particle movement was very strong, resulting in a macroscopically uniform distribution.