title: Grouping behavior of coaxial settling particles in a narrow channel.
abstract: Using numerical simulations, we studied the grouping behaviors of particles settling along their line of centers in narrow channels having a Reynolds number range of 5 ≤ Re ≤ 50. The calculations are based on our previously developed lattice Boltzmann direct-forcing-fictitious-domain method. We report the grouping behavior and investigate the dependence on the number of particles n, the initial interparticle separation h_{0}, and the Reynolds number Re. In particular, the mode of grouping is found to be independent of the number of particles when the Reynolds numbers is small. The two lowermost particles always come together first and form a vertical doublet and then the next two lowest particles form another doublet, and so on. Therefore, we observe n/2 doublets or (n-1)/2 doublets when n is even or odd, respectively. The uppermost particle is always left behind when n is odd. Furthermore, the separation between these doublets remains constant, displaying a power-law dependence decreasing from top to bottom.
authors: Institute of Fluid Mechanics, China Jiliang University, Hangzhou, 310018, China.
authors: Deming
authors: D
authors: Nie
authors: Institute of Fluid Mechanics, China Jiliang University, Hangzhou, 310018, China.|State Key Laboratory of Fluid Power Transmission and Control, Zhejiang University, Hangzhou 310027, China.
authors: Jianzhong
authors: J
authors: Lin
authors: Institute of Fluid Mechanics, China Jiliang University, Hangzhou, 310018, China.
authors: Rongqian
authors: R
authors: Chen