Effects of ridge parameters on axial spreading of droplet impact on superhydrophobic surfaces

Superhydrophobic surfaces decorated with macrostructures have presented remarkable potential in diverse engineering fields, such as aircraft anti-icing. Understanding the effects of the structure shape and size on droplet dynamics is crucial to the design and application of surfaces. Herein, we investigate the maximum axial spreading for droplets impacting on ridged superhydrophobic surfaces with varied ridge shapes and sizes. We propose a mathematical formula to describe the structure shape with profiles quantified by the shape factor, which is easily applied to structure-related studies. The effects of ridge shape and size on the maximum axial spreading coefficient are clarified. The axial spreading of droplets is inhibited by the ridge due to the outward flow of liquid above the ridge tip. The maximum axial spreading coefficient reduces when the ridge becomes sharper, which can be achieved by increasing the shape factor or the ridge height–width ratio. The complex effect of the ridge–droplet size ratio is divided into two regimes according to the shape factor. Furthermore, a prediction correlation of the maximum axial spreading coefficient is established, which involves the coupled effects of all parameters, agreeing well with experimental and simulation results.