Flow of spatially son-uniform suspensions. Part I: Phenomenology

The response of a spatially non-uniform suspension of spheres to several fo rcing agents - forces and torques applied to the spheres, and an imposed si mple shear - is studied numerically for Stokes flow conditions. While the s tandard results are recovered in the uniform case, it is found that the non uniformity of the particle probability distribution gives rise to qualitati vely new features. For example, the rheological behavior of the system cann ot be described solely in terms of an effective viscosity; a relative veloc ity between particles and fluid can arise; the particles can either lead or lag the local angular velocity of the fluid elements. It is shown that a m ixture effective viscosity can be calculated for all three cases with mutua lly consistent results. In a subsequent paper the present results will be u sed to derive in a systematic way closure relations for an averaged-equatio ns description of the suspension. (C) 2000 Elsevier Science Ltd. All rights reserved.