Fedsm 2013-16046 Interaction between a Pair of Drops Ascending in a Linearly Stratified Fluid

In this paper, we provide fully resolved three-dimensional direct numerical simulations of ascending motion of a pair of drops in a linearly stratified fluid using a finite-volume/front-tracking method. We study the density stratification effects on the rise velocity of drops and their stable position for different initial alignments. Due to the formation of a jet in the lee of a single drop rising in a stratified fluid, a decrease in rise velocity (or an increase in drag) is observed compared to the homogeneous case. The hydrodynamic interaction between two drops in a linearly stratified fluid depends on the properties of both fluids and initial orientation of the two drops. For the case of drops rising side by side, the lateral separation of drops is suppressed due to stratification effects. In contrast to homogeneous case, two nearly spherical drops collide with each other at low Froude numbers and oscillate around their neutrally buoyant density level. Two spherical drops rising in tandem in a linearly stratified fluid at finite Reynolds number regime undergo drafting, kissing, and tumbling unlike their counterpart in a homogenous fluid.