Study on dynamic behavior of water droplet impacting on super-hydrophobic surface with micro-pillar structures by VOF method

Abstract

Super-hydrophobic surfaces have been widely developed due to their unique properties, such as adhesion reduction and corrosion inhibition. It is of great significance to explore droplet dynamic process when impacting on super-hydrophobic surface, which can contribute to understanding the mechanism of super-hydrophobicity, and designing self-cleaning surfaces with ultralow adhesion and excellent corrosion resistance. Herein, three-dimensional (3D) numerical model was developed to study the droplet dynamic behaviors on super-hydrophobic NiTi surface. The volume of fluid (VOF) method was carried out to track the multi-phase flow interface and then predict droplet shape evolution during the spreading, retraction, and rebounding stages. In particular, the compression- and stretch-rebounding behaviors were investigated in detail. Based on the results of numerical simulation, the emphasis was placed on the relationship between droplet shape transformation and internal velocity/pressure distribution, revealing the mechanism of droplet morphological evolution during the impingement process. Then the experimental investigations were conducted on the planar and super-hydrophobic NiTi surfaces at different impact velocities to further verify the simulation models. It is indicated that the falling droplet would directly deposit on the planar surface, while it could fully rebound off the pillar-patterned super-hydrophobic surface. Moreover, the motion mechanism of droplet impacting on super-hydrophobic surface was elaborated, which can provide an essential instruction to effectively reduce liquid adhesion and improve anticorrosion ability for the NiTi material.