Journal of Fluid Mechanics

Journal of Fluid Mechanics (2005), 527:141-169 Cambridge University Press
Copyright © 2005 Cambridge University Press
doi:10.1017/S0022112004002903

Papers

Dynamic structure factor study of diffusion in strongly sheared suspensions


ALEXANDER M. LESHANSKY a1 and JOHN F. BRADY a1
a1 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA

Article author query
leshansky am   [Google Scholar] 
brady jf   [Google Scholar] 
 

Abstract

Diffusion of neutrally buoyant spherical particles in concentrated monodisperse suspensions under simple shear flow is investigated. We consider the case of non-Brownian particles in Stokes flow, which corresponds to the limits of infinite Péclet number and zero Reynolds number. Using an approach based upon ideas of dynamic light scattering we compute self- and gradient diffusion coefficients in the principal directions normal to the flow numerically from Accelerated Stokesian Dynamics simulations for large systems (up to 2000 particles). For the self-diffusivity, the present approach produces results identical to those reported earlier, obtained by probing the particles' mean-square displacements (Sierou & Brady, J. Fluid Mech. vol. 506, 2004 p. 285). For the gradient diffusivity, the computed coefficients are in good agreement with the available experimental results. The similarity between diffusion mechanisms in equilibrium suspensions of Brownian particles and in non-equilibrium non-colloidal sheared suspensions suggests an approximate model for the gradient diffusivity: ${\textsfbi D}^\triangledown\,{\approx}\,{\textsfbi D}^s/S^{eq}(0)$, where ${\textsfbi D}^s$ is the shear-induced self-diffusivity and $S^{eq}(0)$ is the static structure factor corresponding to the hard-sphere suspension at thermodynamic equilibrium.

(Published Online March 9 2005)
(Received April 30 2004)
(Revised September 29 2004)



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