Fully-resolved DNS study of rotation behaviors of one and two particles settling near a vertical wall

An immersed boundary technique with multi-direct forcing scheme for fully-resolved direct numerical simulations of multiphase flows is applied to investigate the rotation behaviors of one and two particles settling near a vertical wall in a Newtonian fluid. Some micro phenomena, such as 'anomalous rotation', 'rotation shift' and 'zig-zag' migration are observed for one particle sedimentation, depending on the initial particle position and the mean terminal settling Reynolds number. The 'anomalous rotation' is related to the wall effect, and the 'rotation shift' as well as the 'zig-zag' migration is closely associated with the vortex shedding. For the cases of two particles settling near a vertical wall side by side, the outside particle always rotates anomalously except when vortex sheds from the particle and the 'rotation shift' occurs. But the inside particle may rotate normally or anomalously at the early stage of the sedimentation, depending on the ratio of the initial distance between the two particles to the initial distance between this particle and the wall. For the heavier particle, alternate vortex shedding eventually happens, leading to the 'rotation shift'. Even for the lighter particle without vortex shedding, 'rotation shift' may also appear to the inside particle, which is related to competition between the wall effect and the effect of the outside particle. In addition, it is found that three-dimensionality imposes additional effect on the rotation behaviors of particles. (C) 2013 Elsevier B.V. All rights reserved.