Rising motion of a swarm of drops in a linearly stratified fluid

Direct numerical simulations of a swarm of deformable drops rising in density stratified fluids are presented at intermediate Reynolds numbers. All flow scales are fully resolved using front-tracking/finite-volume method. The average rise velocity and velocity fluctuations of the swarm are reduced in the presence of density stratification. The isotropy in velocity fluctuations is enhanced as the volume fraction increases. The higher likelihood of the cluster formation is illustrated in the presence of density stratification and is explained by quantitative assessment of the microstructure using radial and angular pair probability distribution functions. The combined effect of the drop deformability and density stratification on the average deformation of the drops is investigated. (C) 2014 Elsevier Ltd. All rights reserved.