Direct numerical simulation of droplet collision with stationary spherical particle: A comprehensive map of outcomes

Abstract

We use direct numerical simulation based on the level contour reconstruction method to investigate head-on droplet collisions with dry, stationary, spherical particles. Three important impact parameters are varied over broad ranges: Weber number (4 ≤ We ≤ 150), surface wettability (20° ≤ θeqi ≤ 160°), and droplet-to-particle-size ratio (1/3 ≤ Ω ≤ 2), leading to a total of 225 collision scenarios being examined. Seven collision outcomes are identified: deposition, partial rebound, complete rebound, complete coating, gravity disintegration, momentum disintegration, and splashing, and are represented in outcome regime maps. The first six outcomes are categorized into two cases: the partial-coating case (deposition, partial rebound, and complete rebound for larger particles) and the full-coating case (complete coating, gravity disintegration, and momentum disintegration for smaller particles), with a clear boundary separating the two cases in parameter space. The partial-coating case is characterized by maximum spreading and a subsequent recoiling that depends strongly on wettability. Conversely, the full-coating case involves complete initial wetting of the particle and the following dynamics is strongly governed by impact velocity. Detailed interaction mechanisms of each outcome scenario are also presented. Furthermore, three important quantitative parameters (i.e., film thickness, maximum spreading diameter, and coating time) are analyzed in detail.