On the settling of spherical particles in power-law fluid at moderate Reynolds number

The present paper analyses the settling behavior of multiple spherical particles in a power-law fluid. The results were numerically solved by the lattice Boltzmann method for the fluid mass and momentum equations and the immersed boundary method for the particle dynamics. The transient particle position and velocity data were obtained for a constant Archimedes number of 1000 and density ratio of 2.25. The objects of the investigation were the solid volume fraction, between 0.2% and 3.3%, and the power-law index, from 0.6 to 1.25. The particles repel each other and avoid collision due to increased fluid viscosity in their gaps for the shear-thickening fluid. On the other hand, for shear-thinning fluids, a wake of low viscosity is formed behind the particles, which leads to a high occurrence of particle collisions. However, as the solid volume fraction increases, these effects become less noticeable, mainly because the settling transitions from viscous to collision-dominated. In all cases analyzed, the average terminal velocity was below the terminal velocity of a free particle.