Abstract
The two-dimensional lattice Boltzmann method (LBM) was used to study the motion of two interacting particles with different densities ( and ) and diameters ( and ), which were placed in a vertical channel under gravity. Both the density ratio and diameter ratio () between the particles were considered. The transition boundaries between the regime where the particles settle separately and the regime where the particles interact are identified by and ; they exhibit excellent power-law relationships with . A pattern of horizontal oscillatory motion (HOM), characterized by a structure with a large (but light) particle right above a small (but heavy) one and strong oscillations of both particles in the horizontal direction, was revealed for at intermediate Reynolds numbers. The results indicate that the magnitude of oscillations decreases with , whereas the frequency displays the opposite trend. A sudden increase in the terminal velocity of particles is seen, illustrating a transition from the classical pattern of drafting, kissing, and tumbling to the HOM at a certain . Upon increasing , the pattern of HOM may bifurcate into a vertical steady state at low Re or small . Furthermore, the effects of the confinement ratio and particle-to-fluid density ratio were also examined. The existence of a critical confinement ratio is observed, beyond which the particles interact in a different manner.
14 More- Received 20 June 2020
- Revised 22 December 2020
- Accepted 23 December 2020
DOI:https://doi.org/10.1103/PhysRevE.103.013105
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