  Numerical simulations of positively-buoyant suspension in a horizontally
rotating cylinder were performed to study the formation of radial and axial
patterns. The order parameter for low-frequency segregated phase and dispersed
phase is similar to that predicted for the settling suspension by J. Lee, and
A. J. C. Ladd [J. Fluid Mech., 577, 2007], which is the average angular
velocity of the particles. The particle density profiles for axial bands in the
buoyancy dominated phase shows an amplitude equivalent to the diameter of the
cylinder. Axial density profiles show sinusoidal behaviour for drag dominant
phase and oscillating sinusoidal behaviour for centrifugal force dominant
phase. Results also indicate that the traveling bands are formed as a
consequence of the inhomogeneous distribution of particles arising from a
certain imbalance of drag, buoyancy and centrifugal forces. In the centrifugal
limit, particles move towards the center of the cylinder aggregating to form a
dense core of particles with its axis coinciding with that of the rotating
cylinder, a behaviour which is in contrast to the sedimenting particles. The
particle distribution patterns obtained from the simulations are found to be in
good agreement with the experiments of Kalyankar et al. [Phys. Fluids, 20,
2008].

Soft Condensed Matter