Collective and individual motions of particulate dispersion with concentration interface

细颗粒在液体中的集体运动在水处理或泥沙输送等工程过程中广泛存在。我们研究了粒子在液体中的集体或单独的沉降运动。结果表明，浓度界面是悬浮颗粒与纯流体之间的模糊界面，在这些极端行为中起着重要作用。在小颗粒高浓度情况下，界面不稳定发生在浓度较低的界面，因此沉降速度比孤立颗粒快得多。另一方面，对于浓度较低的大颗粒，浓度界面较不明显，悬浮颗粒单独沉降。结果表明，悬浮物从集体运动到单个运动的转变可以通过浓度界面的边界分辨来控制。

Collective motion of fine particles in liquid can be widely seen in engineering processes such as water treatment or sediment transport. We have studied whether collective or individual settling motion of particles reveals in liquid. The results showed that the concentration interface which is an ambiguous interface between suspended particles and pure fluid plays a significant role in these extreme behaviors. In cases of small particle size with high concentration, the interfacial instability occurs at the lower concentration interface and consequently the settling velocity is much faster than that of an isolated particle. On the other hand, in case of large particles with low concentration, the concentration interface is less distinct and the suspended particles settle individually. We showed that the transition from these collective to individual motions of suspended particles can be controlled by the border resolution of concentration interface.