多颗粒在牛顿流体中沉降的模拟研究

Numerical study of multiple particles sedimenting in a Newtonian fluid

采用格子Boltzmann-虚拟区域方法对多颗粒在牛顿流体中沉降的过程进行了直接数值模拟,颗粒之间的碰撞采用弹性力模型。考察了颗粒初始间距、雷诺数对颗粒沉降形态及沉降速度等的影响。结果表明,奇数与偶数颗粒群的沉降形态及沉降速度差异较大。对于奇数颗粒群(5个),当雷诺数较低时颗粒群呈"凹"形沉降,而当雷诺数增大时中间颗粒会脱离颗粒群,剩下的颗粒群或呈"凹"形或呈"凸"形,这与初始间距有关,文献中仅获得雷诺数较低时的情况。对于偶数颗粒群(6个),当雷诺数较小时呈"凸"形沉降,而当雷诺数增大时颗粒会发生"DKT(DriftingKissing-Tumbling)"现象,且当初始间距增大时发生"DKT"的对象不再是靠近壁面的颗粒对,已有文献中没有观察到这一现象。

Sedimentation of multiple circular particles in a Newtonian fluid has been numerically studied through lattice Boltzmann-Fictitious domain method. The repulsive force model is adopted to deal with particle collision. Effects of initial particle spacing and Reynolds number on the falling patterns and sedimenting velocity are studied. It has been shown that the results of the odd-numbered particles are very different to the even-numbered particles. For the odd-numbered particles, the concave shape of particles is observed when the Reynolds number is low. When the Reynolds number increases, the middle particle eventually separates from the others particles, which exhibit either the concave shape or the convex shape depending on the initial particle spacing. For the even-numbered particles, the convex shape is observed when the Reynolds number is low. When the Reynolds number increases the DKT(Drifting-Kissing-Tumbling) motion happens. Furthermore, it is shown that the DKT does not happen for the pair of particles next to the walls when increasing the initial particle spacing, which is not observed in the existed literatures.