Morphology and wetting characteristics of micrometer-sized droplets impacting rough wall surfaces

Droplet impact on rough walls is a prevalent phenomenon in engineering applications, including surface spraying and spray wetting, and understanding the morphology and wetting characteristics of such impacts is crucial for industrial processes. This study utilizes computational fluid dynamics to examine the effects of velocity, surface tension, and their interactions on the behavior of micrometer-sized droplets impacting rough walls. The findings reveal five morphological changes during droplet impact: oscillation, rebound, bubble formation/rebound, tearing/bubble formation/rebound, and rupture/localized rebound. Droplets with lower surface tension are more likely to rebound in low-speed impacts compared to those with higher surface tension. Surface tension has minimal influence on droplet spreading at the initial stage of impact but significantly affects spreading and retraction prior to the liquid reaching its residual diameter after impact. Lowering surface tension and increasing impact velocity intensify morphological changes and enhance wetting performance on rough wall surfaces. The interaction between surface tension and velocity influences the droplet's behavior, as increased surface tension reduces the enhancement of spreading caused by higher impact velocity, while higher velocity decreases the disparity in the minimum height values of droplets with varying surface tensions. This analysis of droplet morphology and wetting characteristics provides valuable insights for applications involving micrometer-sized droplets interacting with rough wall surfaces in engineering practices.