Inertia- and deformation-driven migration of a soft particle in confined shear and Poiseuille flow

The cross-stream migration of dilute soft particle suspensions under simple shear flow and Poiseuille flow between two parallel plates is investigated with the lattice Boltzmann-immersed boundary method. The competition between particle elastic contraction, fluid shear forces, and fluid inertial stress drives particle migration to a particular steady state position. With a small shear rate, the migration velocity of hard and soft particles is captured by a first order analysis of the Navier–Stokes equation. With a moderate shear flow, the qualitative dependence of the migration velocity and the particle position on the shear rate for both hard and soft particles deviates from the predictions. In a moderate Reynolds number (Re) shear flow, the observed hard sphere migration velocity has a weaker dependence on the Re than predicted and also a higher order dependence on the particle distance from the channel center. For soft spheres, a migration-free zone is observed near the center at a moderate Re and Weissenberg number (Wi). In Poiseuille flow, the soft particle migrates away from the wall to an off-center position dependent on the particle deformation and inertia, in contrast to hard sphere migration where the steady state position is independent of the shear rate.