Numerical simulations of the sedimentation of soft particles in confined Newtonian liquids

The gravitational sedimentation of solid particles in liquids is important in several applications, many of which involve soft particles (e.g., microplastics, microgels, and biological cells). However, there is still little knowledge on the sedimentation of deformable beads. In this work, we employ fully three-dimensional finite-element numerical simulations to investigate the sedimentation of an initially spherical elastic bead in a Newtonian liquid contained inside a square-cross section vessel. In particular, we carry out a wide parametric analysis to understand the effects of inertia, particle deformability, and geometrical confinement on the particle sedimentation dynamics and settling velocity. In addition, the sedimentation of a particle in a Newtonian liquid close to a vertical wall is studied. When the particle sediments at the center of the vessel, the settling velocity increases at increasing inertia and decreases at increasing confinement and deformability. However, at intermediate inertia, the settling velocity passes through a minimum and then rises as the particle gets softer. Correspondingly, the equilibrium deformed shape of the particle shows the appearance of a concavity at the rear. When the sedimentation occurs close to a vertical wall, the closer the particle to the solid surface, the slower its sedimentation. On the other hand, the hydrodynamic interaction between the particle and the wall makes the particle move away from the wall.