Particle simulations using the lattice Boltzmann method.

摘要

This thesis presents an investigation of the physics involved in finite-sized particle transport by means of sedimentation and peristalsis through the use of numerical simulation. In the first part of this thesis, the dynamics of a single two-dimensional elliptical particle sedimenting in a Newtonian fluid is studied. The emphasis here is to study the effect of boundaries on the flow patterns observed during sedimentation. The simulations were performed using a multi-block lattice Boltzmann method as well as a finite element technique, and the results are shown to be consistent. A study of the effects of density ratio, aspect ratio, and the channel blockage ratio is conducted on the flow patterns during sedimentation. As the channel blockage ratio is varied, the results show that there are five distinct modes of sedimentation: oscillating, tumbling along the wall, vertical, horizontal, and inclined sedimentation. The inclined mode is shown to form a smooth bridge between the vertical and horizontal modes. For narrow channels, the mode of sedimentation is found to depend sensitively on the initial orientation of the particle.;In the second part of this thesis, the peristaltic transport of a macroscopic particle in two-dimensional channels and three-dimensional tubes is studied. The effect of the variation of the relevant dimensionless parameters of the system on particle transport is investigated. The particle behavior is examined when the system exhibits the peculiar phenomenon of fluid trapping. Under these circumstances, the particle itself becomes trapped, where it is subsequently transported at the wave speed, which is the maximum possible transport in the absence of a favorable pressure gradient. Finally, the effect of the particle presence on stress, pressure, and dissipation in the fluid is analyzed in hopes of determining preferred working conditions for peristaltic transport of shear-sensitive particles. It is found that the levels of shear stress are most hazardous near the throat of the channel. It is advised that shear-sensitive particles should be transported under conditions where trapping occurs as the particle is typically situated in a region of innocuous shear stress levels.