The change in settling velocity of inertial particles in cellular flow

The gravitational settling of small, spherical inertial particles in a simple, two-dimensional periodic cellular flow is investigated. The effects of adding motions of many length scales and unsteadiness are considered. It is found that in a single length scale steady cellular flow, with square drag law for the equation of motion, when the still fluid settling velocity of the particle V-T <0.5 the average settling velocity of particles (nu(2)) will be larger than V-T by 120%. This occurs because the particles tend to concentrate in downward flow regions. As V-T increases the particles are more uniformly sampling the flow field and hence this uneven distribution of particles is reduced. This uneven distribution of particles is also reduced by adding motion of many length scales and unsteadiness to the flow. In addition, it is found that particles can move in a seemingly chaotic manner without settling into a regular motion even in a steady cellular flow. (C) 1999 The Japan Society of Fluid Mechanics and Elsevier Science B.V. All rights reserved.