Particulate Flow Simulation

The pattern formation in a suspension of 128 settling balls in a horizontally rotating cylinder

A suspension of 128 settling balls in a horizontally rotating cylinder filled fully with an
incompressible viscous Newtonian fluid: 30 < t < 60: three clusters are forming.

The whole cylinder is rotating with angular speed equal to 12.
The length of the cylinder is 4 and its diameter is 1.
The central axis of the cylinder is horizontal and the cylinder two ends are closed.
The dimension of computational domain = (0,1+4h)x(0,4)x(0,1+4h).
The diameter of balls = 0.15.
The density of the ball = 1.25.
The density of fluid = 1; the viscosity = 0.15.
The mesh size for the velocity field = 1/64.
The mesh size for the pressure = 1/32.
The time step=0.001.
The averaged ball speed for 50 < t < 60 seconds is 4.3 (the particle Re=4.3)