Numerical simulation of circular particles migration in oscillatory Poiseuille flow

The present work reports on the simulation of one and two circular particles migration in a two-dimensional channel subjected to oscillatory Poiseuille flow using a finite element arbitrary Lagrangian-Eulerian method. The effects of oscillation frequency on terminal angular velocity, drag force, motion trajectory, vortex structure and relative displacement during sedimentation have been investigated. The results show that the oscillation can cause a strong modification of the eddy formation and shedding behind the particle, and there is a critical oscillation frequency for the flow pattern of particles motion related to the blockage ratio. When the frequency is below the critical value, the single particle increases its rotation speed with alternate oscillation and discharge of vorticity, and eventually approaches the channel wall with one side vortex shedding; otherwise the particle is rotation shift with swinging wake near the channel center. The fluctuating velocities have little impact on the turning couples on the body, while the average vertical velocity decreases with the rising oscillation frequency. Moreover, the hydrodynamic interaction between the particles has a close association with the oscillatory effect. The horizontal distance reaches the maximum and the two particles separate as falling forward at the critical frequency; while the pairs in a low or high frequency oscillatory flow always settle in the horizontal line despite their different rotation characteristics. The final configuration of the pairs is sensitive to the attractor between the particles, and is caused by the Magnus type of lift balancing the wall repulsion and the interplay between particles.