Inertial migration of neutrally buoyant prolate and oblate spheroids in plane Poiseuille flow using dissipative particle dynamics simulations

Abstract

Inertial migration of single neutrally buoyant prolate and oblate rigid spheroids in a plane Poiseuille flow at Reynolds number is studied using dissipative particle dynamics (DPD) simulations. The particles have aspect ratios (ARp, ratio of the major axis L to the minor axis B) from unity to three for prolate and from unity to eight for oblate spheroids, and the ratio of the diameter of the major axis to the gap (L/H) ranges from 0.2 to around 0.4 for both types of the spheroids. The equilibrium positions move closer to the channel center as Re,ARp, and L/H increase. The previously observed effect of the maximum blockage ratio L/H on the equilibrium position is re-confirmed, while differences for oblate vs. prolate shape at fixed L/H, deemed negligible by previous studies, are found in our study to be significant for both the equilibrium position and the rotational behavior, at L/H⩾0.3 and Re⩾200. The major axis of a prolate spheroid generally tumbles in the flow-gradient plane, and the dependence of its focusing position on L/H likely arises from interactions with the wall during tumbling. We observed that when Re is above around 300, with increasing ARp, an oblate spheroid changes from log-rolling with the minor axis in the vorticity direction (ARp=1.5), to inclined-rolling with the minor axis tilted at an angle with respect to the vorticity axis (ARp=3), to a mixed state of inclined-rolling and inclined-tumbling (ARp=5), and finally to an approximate steady state, where the minor axis remains in the flow-gradient plane and slowly fluctuates between 60° and 90° from the flow direction (ARp=8). The utility of the DPD methods for exploring inertial migration phenomena of particles of various shapes is thus demonstrated.