Lattice Boltzmann simulation of two cold particles settling in Newtonian fluid with thermal convection

摘要

The knowledge on the sedimentation of double particles is important in multiphase flow research. However, the available studies almost all are limited on the sedimentation of isothermal particles where there is no thermal convection between particles and fluid. In order to reveal the effects of thermal convection, in the present work the behavior of two cold particles freely settling in vertical channel is investigated using the lattice Boltzmann method (LBM) with direct-forcing immersed boundary method (IBM). By changing the initial separation distance and relative angle between two cold particles, the effects of these initial parameters on the interaction of cold particles settling in Newtonian fluid are also investigated. With different initial separation distance and relative angle between the two cold particles, we find that there are three regimes, namely repulsion, attraction and transition, during the sedimentation. The effects of thermal convection on the interactions between the two cold particles are revealed comprehensively for the first time by making comparisons between sedimentation of the two cold particles and their isothermal counterparts. The results reveal that thermal convection significantly influences the interactions between two cold particles during the sedimentation. The repulsive process will be enhanced due to thermal convection especially when the two cold particles approach each other very close. In addition, we observe the "drafting, kissing and tumbling" (DKT) phenomenon occurs earlier due to thermal convection. Owing to thermal convection, the attraction and repulsion process in the transition regime are enhanced. Moreover, thermal convection enhances the oscillations of trajectories of the two cold particles.