Particulate Flow Simulation

Two balls interact in a bounded shear flow: Return trajectories

In a bounded shear flow of a Newtonian fluid under creeping conditions, two balls moves toward each other and to the mid-plane between two moving walls, and then, they move away from each other and from the above mid-plane. The mass centers switch their initial heights, respectively, after returning.

The dimension of computational domain = (-1.5, 1.5)x(-1,1)x(-0.5,0.5).
The radii of the balls are 0.1.
The density of the balls = 1.
The density of fluid = 1.
The viscosity = 1.
The shear rate = 1.
Top wall moves and the bottom wall is at rest .
The initial mass centers are at (-0.5, 0, 0.0255) and (0.5, 0, -0.0255), respectively.
The mesh size for the velocity field = 1/48
The mesh size for the pressure = 1/24
The time step=0.001.