A Newtonian fluid sheared in the annular region between a rotating inner cylinder and a concentric stationary outer cylinder undergoes various flow transitions. At low inner cylinder Reynolds numbers, the flow is known as circular Couette flow (CCF) which consists of a radially varying unidirectional azimuthal velocity. With the increase in Re, the flow transitions into Taylor vortex flow (TVF) where counter rotating horizontal toroidal vortices fill the annular length. With further increase in Re, TVF transitions into Wavy vortex flow (WVF) where the Taylor vortices gain azimuthal waviness.
Our experiments showed that finite size particles in circular Couette flow (CCF) inertially migrate away from the walls to an equilibrium location at r = ri + 0.4 δ, where ri is the inner cylinder radius and δ is the annular width. And in Taylor vortex flow (TVF), the particles inertially migrate away from the cylinder walls and also away from the vortex core to reach a circular equilibrium region in the cross section of each toroidal vortex. In wavy vortex flow (WVF), the azimuthal waviness of the Taylor vortices did not allow the particles to reach any equilibrium location resulting in uniformly distributed particles in the annular cross section.