title: Oscillations of a solid sphere falling through a wormlike micellar fluid.
abstract: We present an experimental study of the motion of a solid sphere falling through a wormlike micellar fluid. While smaller or lighter spheres quickly reach a terminal velocity, larger or heavier spheres are found to oscillate in the direction of their falling motion. The onset of this instability correlates with a critical value of the velocity gradient scale Gamma(c) approximately s(-1). We relate this condition to the known complex rheology of wormlike micellar fluids, and suggest that the unsteady motion of the sphere is caused by the formation and breaking of flow-induced structures.
authors.affiliation: The W. G. Pritchard Laboratories, Department of Mathematics, Penn State University, University Park, Pennsylvania 16802, USA.
authors.forename: Anandhan
authors.initials: A
authors.lastname: Jayaraman
authors.forename: Andrew
authors.initials: A
authors.lastname: Belmonte