Numerical investigation on lamella behaviors in droplet impingement on surface: influence of surface wettability

The effect of wettability on lamella behavior during droplet impingement on flat surfaces is investigated by detailed numerical simulations with different contact angle parameter sets. The coupled level set and volume of fluid method (CLSVOF) incorporated with a dynamic contact angle model and the contact angle imposing method is implemented to account for the wetting dynamics of the droplet on the surface. The numerical framework is extensively validated by comparing the droplet impingement behavior with the experimental results, qualitatively and quantitatively. The results show that an increase in the difference between the advancing contact angle and the equilibrium contact angle can trigger repulsion of the lamella on the surface, which can result in subsequent cusp generation and rim destabilization. Similarly, when the difference between the advancing contact angle and the equilibrium contact angle is kept constant, rim destabilization can also be triggered solely by increasing the equilibrium contact angle. Such destabilization contributes to enhanced ligament generation. Additionally, increasing the equilibrium contact angle significantly enhances rim destabilization by increasing the advancing contact angle on surfaces with equilibrium contact angles below 90◦. The differences in lamella breakup behavior due to the variation in surface wettability are attributed to the dominant effect of wettability on the splashing angle during impingement. The findings in this work would help to elucidate the effect of wettability on impinging droplets and thereby offer guidance for designing surfaces that enable the manipulation of droplet behavior during impingement.