Inertial migration of soft particles initially evenly spaced along the flow direction in a channel

Abstract

The inertial migration of two-dimensional soft particles initially distributed uniformly in channel flow is numerically studied by employing an immersed-boundary lattice Boltzmann method coupled with a finite element method. To model a soft particle, a capsule with an elastic membrane separating the liquid inside from the outside is used. Validation tests show excellent agreement with previous numerical results of other researchers. Then, the effects of the number of capsules Np, the bending stiffness Eb, the initial position [Formula: see text], and the Reynolds number Re on the dynamics of the capsules in channel flow are investigated in detail. Interestingly, we discover a new regime (labeled as regime E) in which a few capsules situated near the channel centerline travel much faster than the rest. Moreover, regime E is more prone to vanishing while the capsules are very soft. The normalized overall lateral position of the capsules σ increases almost linearly with Np when the capsules stabilize in a single-line particle train (designated as regime A). We also make an effort to explain the formation of the capsule deformation shape in regime A. The steady dynamics of a single capsule depend on whether the initial position is on the channel centerline. However, if the capsule is not released on the channel centerline, the steady capsule dynamics are independent of the initial position. But, it is not true for multiple capsule dynamics. These findings may help understand the inertial migration of capsules in channel flow.