| Particulate flow of solids in fluids occur in a variety of settings, e.g. sedimenting and fluidized suspensions, lubricated transport, composite materials, polymers, proteins, etc. The suspending fluid can be Newtonian or non-Newtonian depending on the application. Many times the non-Newtonian suspending fluid exhibits viscoelastic properties. Consequently there are various mechanisms at work depending on the type of problem being considered. The primary focus of this dissertation is to study the dynamics of a suspension of non-Brownian circular rigid particles in Newtonian and viscoelastic fluids using two-dimensional finite element simulations. Interparticle colloidal forces are not considered. Direct numerical simulation of solid-liquid flows with a large number of solid particles is greatly restricted by the computational cost. Hence it is necessary to use periodic boundary conditions to deal with relatively less number of particles. An unstructured mesh generation scheme, which can generate a mesh in such periodic domains, is developed. Numerical simulations are performed to identify the mechanisms important in the formation and breaking of chain structures of particles sedimenting in viscoelastic fluids. Various flow regimes are identified for pressure-driven flow of particles in Newtonian and viscoelastic fluids. Issue of rheological modeling of a suspension of neutrally buoyant solid particles in Newtonian and viscoelastic fluids is addressed. Fundamental differences in the rheology of suspensions in Newtonian and viscoelastic fluids are identified. In the end we consider the problem of electroosmosis which deals with sub-micron size charged species suspended in a Newtonian fluid. A different numerical scheme is used to solve this problem. |
