Study of gravitational sedimentation of two flexible circular shaped particles using Immersed Boundary Method

This work numerically illustrates the Drafting, Kissing, and Tumbling (DKT) phenomena between two flexible, interacting, and circular particles in a bounded medium. The original Immersed Boundary (IB) Method was employed to conduct the study in a two-dimensional setup for different fluid viscosities. Two scenarios were considered: in one, the interacting particles were assumed to have the same flexibility, whereas in the other, the particles had different flexibility. The study attempted to explore the impact of flexibility on the dynamics of particles. For the same flexibility case, we observed multiple DKTs for higher flexibility cases and wobbling motion for the less flexible case in a less viscous fluid medium. For a higher viscous fluid medium, we observed drafting phase only. In the case when the leading particle was made more flexible than the trailing particle, irrespective of any flexibility and fluid viscosity of the particle, their configuration status was retained, i.e., the leading particle remained leading, and the trailing particle remained trailing. In the case when the leading particle was less flexible than the trailing particle, for a higher viscous fluid medium, the particles experienced drafting and kissing only, but for a lower viscous fluid medium, the particles had one cycle of DKT. The results obtained are physically justified.