On instabilities and migration phenomena in cone and plate geometry

This paper reports experimental observations on suspensions of glass spheres in a viscoelastic polymer solution. The fluid is submitted to shear flows at constant stress in a cone and plate geometry. After shearing, for sufficiently high stress, one observes, on the plate and on the cone, that the beads are located on concentric rings. In each ring, they regroup in regularly spaced small packs. This migration phenomenon is related to the viscoelasticity of the suspending medium but the mechanism of formation of the packs is not yet elucidated.