基于DPM模型求解自由下落颗粒羽流卷吸空气量

为深入了解自由下落颗粒羽流卷吸空气的特性，对氧化铝颗粒从出口直径为5 mm的圆形孔中自由下落的气固两相流场进行了数值模拟研究。依据RNG k-ε模型求解气相雷诺时均N-S方程并进行离散化处理，采用DPM模型跟踪单个粒子以求解颗粒的运动方程，并通过SIMPLE双向耦合，对自由下落颗粒羽流流动特性进行数值模拟。结果表明：自由下落颗粒羽流卷吸空气气相速度在羽流中心线上处于最大值，随着径向距离的增大速度值明显地减小，直到距离中心线30 mm处，之后速度的变化趋于稳定；颗粒在净质量力作用下沿质量力方向首先作加速运动，之后下落速度up随着下落高度的变化趋于平缓，羽流末端颗粒运动基本遵守颗粒自由沉降规律；羽流卷吸空气量随着下落高度的增加而增大，其规律与颗粒群模型给出的结果高度吻合。通过比较分析发现，采用DPM模型很好的解决了对颗粒相运动方程的求解并可获取颗粒运动轨迹，对于自由下落颗粒羽流特性的分析不失为一种有效而可行的方法。

Solving plume air entrainment of free-fall particles based on DPM model

In order to explore the air entrainment characteristics of free falling particles, a numerical simulation was carried out for a free falling particle plume of alumina particles through a circular hole with a diameter of 5 mm. An Renormalization-group(RNG) k-ε model was used for a solution of Reynolds averaged equations and its discretization. A DPM model was applied to trace a single particle to solve the particle motion equation. Then, by SIMPLE two-way coupling, a numerical simulation of the flow characteristics of a free falling particle plume was conducted. The results showed that the velocity of the entrained air by the free falling particle plume can reach a maximum value along the plume centerline. Also, as the radial distance increases, the velocity clearly decreases within a distance of 30 mm far from centerline. After that, the variation trend becomes stable. Under the action of net mass force, particles move at an accelerated rate, and then, the falling velocity up slightly changes. At the end of the plume, a particle basically follows the law of free falling particles. The entrained air quantity increases as the falling height increases, which agrees well with the results obtained by the particle population model. Through a comparative analysis, we determined that the DPM model can solve the particle motion equation very well and can obtain the particle motion trajectory. Thus, it is an effective and feasible method to analyze the plume characteristics of free falling particles.