Rigid spheroid migration in square channel flow of power-law fluids

The characteristics of rigid spheroid migration in square channel flow of power-law fluids are numerically investigated by the three-dimensional lattice Boltzmann method. The effects of aspect ratio (alpha), blockage ratio of the particle (k), power-law index (n) and Reynolds number (Re) of the fluid on the inertial migration of rigid prolate and oblate spheroids are explored, respectively. The results show that the shear-thinning fluid with large fluid inertia is beneficial for fast focusing rigid particles to the equilibrium positions in square channel. There are two stages of particle migration and four stable channel face equilibrium positions for migration of spheroid; the channel corner equilibrium positions only exist for the oblate spheroid under a low inertia effect. The prolate spheroid exhibits tumbling and log-rolling (LR) rotational modes, and the LR mode is conditionally stable. For the oblate spheroid, only the LR mode exists when Re is large while two new rotational modes are captured when Re decreases. The equilibrium position of the prolate and oblate spheroids increase when alpha < 1.0 then decrease at larger alpha values, escaping the channel centreline with decreasing n and k and increasing Re. The changes of in-ertial focusing length, angular velocity, and rotational period of the spheroid are systematically analysed to study mechanism of spheroid migration. The current results enrich our understanding of rigid particle accumulation behaviour in channel flow of non-Newtonian fluids and may also shed light on how to efficiently focus and control particles in microfluidic devices.