Interactions between two deformable droplets in tandem subjected to impulsive acceleration by surrounding flows

Abstract

AbstractThe dynamics of two deformable drops placed in tandem and subjected to a sudden acceleration by a gaseous flow is investigated. A finite-volume scheme coupled with the method of moving mesh interface tracking is employed. The unsteady interactions between the droplet pair are studied by varying the minimum initial separation distance (${d}_{0} $) from $0. 6{r}_{0} $ to $10{r}_{0} $ with ${r}_{0} $ being the radius of the initial spherical droplets. The influence of the interactions on the droplet dynamics is examined by comparing with the case of a single isolated droplet at three initial Weber numbers ${\mathit{We}}_{s, 0} $ of 40, 4 and 0.4. The computations show that for small initial separation distances the dynamics of the downstream droplet is significantly affected by the presence of the upstream droplet. A mushroom shape is formed by the droplet pair at the two largest Weber numbers, while the two drops experience small deformation and shape oscillations at ${\mathit{We}}_{s, 0} = 0. 4$. The drag coefficient of the downstream droplet is dramatically reduced, especially for the two largest Weber numbers with smaller initial separation distances due to the sheltering effects, while the drag force of the upstream drop is slightly decreased. For the cases with smaller ${d}_{0} $, a thin film is formed between the two drops at the later stages, and this leads to a sudden increase in the drag of the trailing drop, but a sharp reduction in the drag of the leading drop.