| 26 Jan 2026
Numerical study of the collection of aerosol particles by falling deformable drops
Abstract. The free fall of a drop through gas loaded with solid particles gives rise to multiple physical interactions, which remain poorly documented, esp. 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 number such that drops present deformations/oscillations or not (e.g., Re = 30, 70, 500 and 876). An 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/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.
The wet removal of aerosol particles from the atmosphere, i.e. their collection by cloud droplets and raindrops, is a highly efficient atmospheric cleansing process. This scavenging mechanism is of crucial importance in heavily polluted industrial regions; moreover, in the case of nuclear accidents or volcanic eruptions, the removal of hazardous particles from the atmosphere has significant health and economic implications. Therefore, the topic of the present manuscript is highly relevant not only for the aerosol community but also for the broader atmospheric physics and chemistry communities.
Experimental investigations of scavenging processes are challenging, and the results are often uncertain due to difficulties in accurately characterising aerosol size distributions and environmental parameters such as temperature and humidity. In addition, drop size plays a key role in determining scavenging efficiency. For these reasons, numerical investigations are often preferred for studying this problem. However, such numerical tools must be both accurate and computationally efficient. This is one of the main objectives of the authors of the present manuscript, who introduce a model to numerically investigate the dynamics of freely falling water drops in air laden with aerosol particles.
In general, the paper is very well written, easy to read and to follow the concept. I recommend the manuscript for publication in Aerosol Research. I have really just a few comments and remarks before publication:
First a structural suggestion: Please consider to move some part from the Discussion and conclusions section to the Results section. It is more common to have a Results and Discussion section and a stand-alone Conclusion section. The discussion of the results fits there better.
Minor issues: