Transport of a dilute particle suspension through a sharp density interface*

This study explores the dynamics of particle transport in density-stratified fluids, a phenomenon frequently observed in oceans. An immersed-boundary technique is employed for particle-resolved numerical simulations within a 3D Cartesian domain. The simulations are conductedin a quiescent, sharply-stratified fluid environment within a computational domain of size 12 D_p x 12 D_p ×36 D_p,where D_p=250 μm signifies the diameter of the spherical particles. These particles are modelled using a fictitious domain method, with a no-slip condition at their surfaces. The settling dynamics are governed by the Galilei, Froude, and Prandtl numbers. The stratification strength is characterized by Γ=(ρ₂−ρ₁)/(ρ_p−ρ₁) where ρ₁and ρ₂ representing the undisturbed fluid densities above and below the stratification interface, respectively. Initially, the particles are evenly distributed and fully immersed in the top fluid, with some distance away from the domain boundaries and the density interface. Numerical results that the influence of Γ on the suspension's settling patterns through the density interfaceare reported. The effect of varying the Prandtl numbers on the settling for temperatureand salinity-stratified fluids, and the influence of the Galileinumberare also examined. Finally, this study also examines  the impact of varying individual particle sizes within a particle suspension, and the height of the density transition layeron the collective transport of the suspension.