A numerical investigation of droplet bouncing behaviors on dual micro-structured superhydrophobic surfaces

Abstract

An in-depth study of the droplet bouncing behavior and microscopic mechanism on superhydrophobic surfaces containing different micro-structures is of great significance in the power production and transmission fields. In this study, the lattice Boltzmann method with multiple relaxation times (LBM-MRT) was used to investigate the droplets bouncing process on superhydrophobic surfaces. Three groups of novel superhydrophobic surface microstructures were developed based on the protrusion/recess dimensions of columnar structures and the distribution positions of randomly rough microstructures. All randomly rough micro-structures were characterized by skewness (−1.1 to 1.1), kurtosis (1.0 to 5.0) and standard deviation (0.3 to 1.1). The basic morphology and roughness parameters of the randomly rough micro-structures were extracted using atomic force microscopy (AFM). In turn, the various types of surfaces required for numerical simulations were obtained by numerical reconstruction methods. Use liquid-gas density ratios of 800 and gas-liquid dynamic viscosity ratios of 10, which are extremely close to the corresponding parameters for air and water. After experimental validation, the droplet bouncing dynamics were compared and summarized. The maximum spreading length, total contact time and post-bounce morphology of the droplets during the bouncing process were analyzed. The results shown that column with a spacing of 30 μm was able to produce the maximum radial spreading tendency of the droplets. On the P-R-R surface, the increase in the columns spacing reduced the drop rate of total contact time from 9.04 % to 5.89 % and then increased to 7.35 %. Droplets bounced best on surfaces with relatively uniform overall morphology and relatively fewer excessive spikes and deep valleys. The specific parameter ranges satisfy skewness −0.5 to 0.3, kurtosis 3.0, and standard deviation 0.3 to 0.5. Based on data of droplets bouncing on typical surfaces, we also summarize empirical equations for the relationship between maximum spreading length and total contact time and skewness. The regularities obtained in this paper on the effect of dual micro-structures on the dynamic behavior of droplets may contribute to the in-depth optimization of superhydrophobic surfaces.