|Ph.D Student||Seiden Gabriel|
|Subject||Banding of Suspended Particles in a Rotating Horizontal|
|Department||Department of Physics||Supervisors||Professor Emeritus Stephen Lipson|
|Professor Emeritus Marius Ungarish|
Non-Brownian particles suspended at low volume concentration in a rotating horizontal cylinder filled with a low-viscosity fluid are observed to segregate into well-defined periodic axial bands. Under some conditions the observed pattern oscillates between two possible band configurations. An experimental investigation of the dependence of the phenomenon on particle characteristics (i.e. dimensions, shape and specific gravity), tube diameter and length, and fluid viscosity is presented. A theoretical explanation of the phenomenon is proposed, in which the segregation occurs as a result of mutual interaction between the particles and inertial modes excited in the bounded fluid. This leads to the result that macroscopic suspended particles accumulate in alternate nodes of the mode excitation, which is in agreement with the experiments, and leads to two degenerate band patterns observed for each mode. A confirmation of the theoretical approach was obtained by means of a photographic capture of the flow field resulting from the inertial mode, and by numerical simulations of the axial migration tendencies of the solid particles given the theoretical flow field. The numerical simulations also allowed for a stability analysis of the band patterns in the appropriate dimensionless parameter space, revealing the boundaries of the stability region. An explanation of the related phenomenon of oscillations between two allowed states is presented, whereby the oscillations result from near-resonant amplitudes, which render the band configuration unstable. The banding phenomenon and oscillations were also observed to occur in the configuration of a rotating horizontal tube having a square cross section.