Experimental Investigations and Direct Numerical Simulations of Rigid Particles in ShearFlows of Newtonian and Complex Fluids

The main objective of this dissertation is to provide well-resolved data to understand the dispersion of solid in inhomogeneous shear flows. To this end, accurate experiments and high-fidelity computations are performed. On the experimental front, the dispersion of solid in curvilinear flows of Newtonian fluids is studied. The results show that in the absence of inertia, drag forces on the particles play an essential role in the dispersion of solid. Therefore, the first step to study the dispersion of solid in flows of non-linear or complex fluids is to determine drag forces on a particle when a stream is present normal to the mainstream flow direction. This gap in knowledge has established the computational part of this research. A summary of the performed research is as follows. Three-dimensional numerical simulations were performed to investigate the sedimentation of a single sphere in the absence and presence of a simple cross shear flow in a yield stress fluid with weak inertia. In our simulations, the settling flow is considered to be the primary flow, whereas the linear cross shear flow is a secondary flow with amplitude 10% of the primary flow. To study the effects of elasticity and plasticity of the carrying fluid on the sphere drag as well as the flow dynamics, the fluid is modeled using the elastovisco-plastic (EVP) constitutive laws proposed by Saramito [Sar09]. The extra non-Newtonian stress tensor is fully coupled with the flow equation and the solid particle is represented by an immersed boundary (IB) method. Our results show that the fore-aft asymmetry in the velocity is less pronounced and the negative wake disappears when a linear cross shear flow is applied. It is found that the drag on a sphere settling in a sheared yield stress fluid is reduced significantly as compared to an otherwise quiescent fluid. More importantly, the sphere drag in the presence of a secondary cross shear flow cannot be derived from the pure sedimentation drag law owing to the non-linear coupling between the simple shear flow and the uniform flow. Finally, it is shown that the drag on the sphere settling in a sheared yield-stress fluid is reduced at higher material elasticity mainly due to the form and viscous drag reduction.Particle migration in a non-Brownian suspension sheared in a Taylor-Couette configuration and in the limit of vanishing Reynolds number has been experimentally investigated. Highly resolved index-matching techniques are used to measure the local particulate volume fraction. In this wide-gap Taylor-Couette configuration, it is found that for a large range of bulk volume fraction, phi_b= 20%-50%], the fully developed concentration profiles are well predicted by the Suspension Balance Model (SBM) of Nott & Brady [NB94]. Moreover, systematic measurements of the migration strain scale and of the migration amplitude are provided which highlight the limits of the SBM predictions. Finally, the wall-effects on the particle migration in a non-Brownian suspension sheared in a wide-gap Taylor-Couette cell are studied experimentally. This was performed by covering the inner and outer cylinders with bumpy rough surfaces. Highly resolved index-matching techniques are employed to measure the local particulate volume fraction. It is found that the effect of particle layering is diminished due to imposing bumpy rough boundaries. Moreover, the migration dynamics, strain scale, and amplitude are greatly affected by the structuration of the suspension.