Swapping trajectories: a new wall-induced cross-streamline particle migration mechanism in a dilute suspension of spheres

• Published in: Journal of fluid mechanics Vol. 592; pp. 447 - 469
• Main Authors: ZURITA-GOTOR, M., BŁAWZDZIEWICZ, J., WAJNRYB, E.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 10.12.2007
• Subjects: Diffusion; Exact sciences and technology; Fluid dynamics; Fluid mechanics; Fundamental areas of phenomenology (including applications); Laminar flows; Laminar suspensions; Mathematics; Mechanical engineering; Multiphase and particle-laden flows; Nonhomogeneous flows; Physics; Shear loading; Streamlines; Shear flow; Particle motion; Digital simulation; Creeping flow; Trajectories; Particle suspension; Relative motion; Dilute suspension; Two-phase flow; Modelling; Wall effects; Spherical particle
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/S0022112007008701

Binary encounters between spherical particles in shear flow are studied for a system bounded by a single planar wall or two parallel planar walls under creeping flow conditions. We show that wall proximity gives rise to a new class of binary trajectories resulting in cross-streamline migration of the particles. The spheres on these new trajectories do not pass each other (as they would in free space) but instead they swap their cross-streamline positions. To determine the significance of the wall-induced particle migration, we have evaluated the hydrodynamic self-diffusion coefficient associated with a sequence of uncorrelated particle displacements due to binary particle encounters. The results of our calculations quantitatively agree with the experimental value obtained by Zarraga & Leighton (Phys. Fluids, vol. 14, 2002, p. 2194) for the self-diffusivity in a dilute suspension of spheres undergoing shear flow in a Couette device. We thus show that the wall-induced cross-streamline particle migration is the source of the anomalously large self-diffusivity revealed by their experiments.