Numerical study of the collection of aerosol particles by falling deformable drops

The free fall of a drop through gas loaded with solid particles gives rise to multiple physical interactions, which remain poorly documented, especially when the drop is no longer spherical. In particular, no model predicts the particle collection efficiency for drops undergoing deformations or oscillations. This study aims to contribute to this effort by investigating numerically the dynamics of water drops freely falling in air laden with dispersed solid particles for drop Reynolds and Weber numbers such that the drops do (or do not) deform or oscillate (e.g., Re=30, 70, 500, and 876). A Eulerian–Lagrangian framework is adopted. The drop internal and external flows are simulated with direct numerical simulation (DNS), and the dynamics of the liquid–gas interface are tracked using a combination of the volume of fluid (VOF) and level set methods; this approach predicts the interface dynamics in line with experimental data. The trajectories of solid particles are simulated using Lagrangian tracking and taking into account drag, gravity, and Brownian motion. For spherical drops with Reynolds numbers below 200, our methodology replicates previous results. In the presence of oscillations and/or deformations, the flow parameters of the two continuous phases are correctly predicted. The particle collection efficiency also follows the experimental trend, but the values differ significantly from measurements found in the literature. We therefore propose certain areas of improvement with the goal of obtaining better fits to the available experimental data.