RHEOLOGY OF A SUSPENSION OF NEUTRALLY BUOYANT SOLID CIRCULAR PARTICLES IN NEWTONIAN AND VISCOELASTIC FLUIDS

摘要

It is necassary to study the rheology of suspensions to understand its behavior when subjected to various flow conditions. Considerable theoretical effort has been made to model the macroscopic properties of a suspension of rigid particles in a Newtonian fluid, but for most part, it has been limited to zero particle Reynolds number. Investigation of the rheological behavior of suspensions in non-Newtonian fluid has not progressed as much as it has for suspensions in Newtonian fluid. In this paper we have studied the macroscopic properties of a suspension of rigid circular particles in Newtonian and Oldroyd-B fluids in the dilute limit (no interaction between particles) by performing two-dimensional finite element simulations. The numerical scheme solves the entire fluid momentum equation without neglecting any terms. The particle-fluid mixture was subjected to uniform shear flow between two parallel plates. The forces acting on the particles were purely hydrodynamic. It was seen that the suspension of particles in Newtonian fluid shear thickens. The first normal stress difference was negative and increased in magnitude as the Reynolds number was increased. We also observed that the particle contribution (due to the hydrodynamic force acting on them) to the bulk stress of the suspension of rigid particles in an Oldroyd-B fluid shear thins. Oldroyd-B fluid itself does not show any shear thinning behavior. The first normal stress difference was positive and increased as the Reynolds number was increased. Shear thinning and the increase in the first normal stress difference was enhanced as the elasticity of the fluid was increased.