Interaction between in-line spheroids settling in a linearly stratified fluid*

This study explores the transport of solid particles in density-stratified fluids. In oceans, particles and marine snow fall through fluids with notable density differences caused by variations in salinity and temperature. Such heterogeneity in the background fluid influences the settling or rising rates of particles, often causing them to accumulate at transitional density layers. Previous research has mainly examined spherical particles, focusing on their isolated motion, pairwise interactions, and collective transport in stratified fluids. This research, however, extends the investigation to the interaction between two spheroidal particles settling in-line in a stratified fluid.The study employs an immersed-boundary technique to conduct particle-resolvednumerical simulations in a 3D Cartesian domain. The spheroidal particles, initially at rest and vertically aligned, are placed in a quiescent, linearly-stratified fluid within a 12D_p×12D_p×24D_p computational domain, with D_p=250 μm as the equivalent spherical particle diameter. The shape of the spheroids is determined by their aspect ratio A/R=b/aa nd they are modeled using a fictitious domain method with a no-slip condition on their surfaces. The study is governed by the Galilei, Froude, and Schmidt numbers. The results demonstrate the effects of varying the stratification strength through the Froude number, the particles' aspect ratios, and the initial separation distance between the particles on the interaction dynamics between the settling spheroids.This work further considers the effect of smaller Schmidt numbers, relevant for thermally stratified fluids, and of increasing the particle size to investigate the effects of particle inertia on the settling and interaction dynamics.