Axial Band Formation in a Rotating Suspension

The simulations show that the dynamics the suspension are characterized primarily by the dimensionless frequencyW* = W d/U, where d = n^-1/3 is the mean interparticle spacing, which is the characteristic length in the low-frequency phases. There is a dynamic phase transition separating a segregated phase, Figs. 1(a) and 1(b), from a dispersed phase, Fig. 1(d). Axial bands are formed in the transition region W* ~ 1, Fig. 1(c). When viewed from the top we see bands of high and low concentration, with a spacing approximately equal to the diameter of the cylinder. From the front we see angled bands due to the effects of the secondary flow, which can be clearly seen in the video clip. A discussion of these results can be found in Refs. [1] and [2].

Axial band formation in a rotating suspension. Over a narrow range of rotation rates around Ω* ~ 1, an initially uniform particle distribution is unstable and permanent axial perturbations develop in the particle concentration. The figure shows typical particle distributions when viewed from the top (upper) and front (lower) of the cylinder. The blue-colored particles are moving to the right while the yellow particles are moving to the left.

A video clip showing the band formation can be found here (3.4 MByte AVI-DivX). Particles have been colored according to whether they are moving to the right (blue) or left (yellow).