Direct Simulations of Fluid-Particle Flow in Newtonian and non-Newtonian Fluids Using Coupled Lattice Boltzmann and Discrete Element Methods
Date
2021-09
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Abstract
Coupled lattice Boltzmann and discrete element methods are employed to investigate a suite of fluid-particle flow problems in both Newtonian and non-Newtonian fluids. First, the rheological properties of finer particle suspensions in a Newtonian fluid are investigated, as the particle shape and solid fraction vary. An increase of the relative viscosity is observed when the particles become more oblate, accompanied by an increase of particle contacts and contact distance. Particle reorientation is seen to occur systematically in denser oblate particle suspension subject to the shear flow. A connection between the micro-structure statistics and the suspension viscosity is proposed. Second, the shear rate effects on the finer oblate particle suspension viscosity are studied. The viscosity of the suspension is observed to decrease under a higher shearing rate due to the reduction of the inter-particle friction coefficient, resulting in the shear-thinning behavior of the suspension. Finally, the sedimentation of a granular particle cloud in shear-thinning suspensions is investigated, as the rheology of the suspension, Reynolds number, and particle cloud concentration vary. At higher Reynolds numbers, the particle cloud length grows in the direction of settling and reaches a quasi-steady state. The ratio of the particle cloud quasi-steady settling velocity to the single-particle terminal velocity in the same fluid, increases when the cloud settles in the shear-thinning suspensions. This velocity increase is more significant at a low Reynolds number. At even lower Reynolds numbers, the cloud loses its initial shape and disintegrates while settling, with particles escaping from the cloud due to differential particle settling velocities.
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Keywords
Lattice Boltzmann method, Discrete element method, Particle suspension rheology, Oblate particle suspension, Viscosity and normal stress differences, Particle cloud settling, Shear-thinning rheology
Citation
Guo, J. (2021). Direct simulations of fluid-particle flow in Newtonian and non-Newtonian fluids using coupled Lattice Boltzmann and discrete element methods (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.