Physics of fluids Volume 11 number 3 Mars 1999

Dynamics of non-Brownian rodlike particles in a nonuniform elongational flow

M. Cloitre

Laboratoire Mixte CNRS ELF-ATOCHEM. 95 Rue Danton, 92303 Levallois-Perret. France

A. Mongruel

Laboratoire GEMICO, ENSIC, 1 Rue Grandville, 54000 NanC:'., France

(Received 5 February 1998; accepted 30 November 1998)

This paper deals with the orientation of non-Brownian rodlike particles in a nonuniform elongational flow at low-Reynolds number. Experimentally, an elongational flow is created by ir'roducing a small circular orifice into a cylindrical channel. The flow field is studied using a tracer anemometry technique. On the axis of symmetry , the deformation field is that of a pure elongation with a nonuniform tlongation rate. It is weIl des.cribed by the analytical solution obtained for an infinite contraction ratio. This flow is used to study the dynamics of non-Brownian rodlike particles subject to nonuniform elongation. The orientation dynamics of a particle depends on the history of the deformation that it has experienced. The effects of small perturbations existing in the vicinity of the orifice are greatly amplified downstream. Consequently, particle motion does not exhibit the symmetry with respect to the orifice which is expected at low-Reynolds number. <9 1999 American lnstitute of Physics. [S 1 070-6631 (99)01903-0]