Effect of confinement on the rotation of a two-dimensional elliptical porous particle in shear flow

Abstract

The rotation of non-spherical porous particles in fluid flows is of practical relevance in various natural and industrial processes. However, despite the increasing interest in micro-scale channels and reactors, the understanding of rotation of non-spherical porous particles in a confined fluid flow is, if not blank, far from complete. In this work, we present a numerical study on the rotation of an elliptical porous particle in a confined shear flow by solving the governing equations using a lattice Boltzmann method. The particles with varying aspect ratios AR, Darcy number Da, and Reynolds number Re are examined for different confinement ratios B. Akin to its solid counterpart, the elliptical porous particle either exhibits time-periodic rotation with a non-uniform angular rate or takes a stationary orientation for different B. With finite fluid inertia, both the maximum and minimum angular rate decrease with B. For the elliptical porous particle, a higher B promotes the increasing rate of rotation period against Re, resulting in a smaller critical Reynolds number Rec (if observed) at which the particle ceases to rotate. A scaling law for solid particles was extended to correlate the rotation period and Re for porous particles, where B has a negligible effect. An empirical formula to predict Rec as a function of B, AR, and Da is established using the symbolic regression. The transition from rotating to stationary at different B can be explained by the net torque exerted on the elliptical porous particle.