Lattice Boltzmann simulations of dense granular suspensions

This thesis aims to understand, via lattice Boltzmann simulations, the rheological behaviour of charged monodisperse particle suspensions in hydraulic transport lines. Therefore, a three-dimensional, in-house numerical code was implemented using an immersed boundary-lattice Boltzmann method (IB-LBM) to assess the rheology and suspension structures subjected to constant and time-varying shear flows, for a wide range of solids volume fractions, 2% ≤ φv ≤ 52%, and particle Reynolds numbers, 0.1 ≤ Rep ≤ 0.5. The particles translate, rotate, and collide under the influence of applied shear and sub-grid scale forces and torques. Preliminary simulations of suspensions began by simulating uncharged particles with a spring force model under constant shear rate. The simulations revealed shear-thickening, and the relative apparent viscosity showed excellent agreement with the literature for Rep = 0.11. For higher values of φv and Rep, apparent discrepancies in the viscosity were observed due to slower particle rotation and increased clustering. The sub-grid scale force model was improved by replacing the spring forces with the corrections for the unresolved lubrication (normal and tangential) forces and electric double layer (EDL) forces. When the collisions were modelled with lubrication corrections, the contribution of the tangential lubrication corrections to the suspensions’ viscosity was dominant, and the particles assembled to form homogeneous chain-like structures. By subsequently adding EDL forces, the chain structures were broken and the viscosity of the suspensions was decreased down to ≈ 30% due to the formation of hexagonal assemblies. The response of suspensions subjected to instantaneous flow reversals with lubrication correction and EDL forces revealed that the presence of EDLs shortens the time required for suspensions to attain equilibrium. The investigation of the suspensions’ behaviour due to step increases and decreases in shear rate magnitudes showed that when sheared continuously, dense suspensions retain their previous shear history but lose their previous state when the fluid flow was suddenly stopped and resumed.