Impacts of particle shape on sedimentation of particles

Abstract

The effects of particle shape on settling behavior of sand particles under the influence of gravity in an initially quiescent water environment have been studied by a two-dimensional high-resolution numerical experiment. The numerical method is based on an immersed boundary method. The accuracy of the code is well demonstrated against experimental data of a fluttering rectangular plate. The particle is either elliptical or rectangular of size about 1 mm, and the particle aspect ratio is varied without changing the volume. The particle-to-fluid density ratio is chosen to be 2.65, and the resulting Galileo number is about 127. It is found that the terminal settling velocity tends to decrease with an increase in the aspect ratio and that the settling velocity of a rectangle is always lower than that of the corresponding ellipse in both the isolated and multiple particle systems. While the presence of surrounding particles makes the influence of the particle shape less clear, the circular particle still presents significant differences in the terminal settling velocity compared with the other particles. It, therefore, calls for caution in the spherical assumption of particle shape and encourages a deeper understanding of the particle shape effects.