Title : Interface deformation on super-hydrophobic surfaces in extreme conditions
Contact : Nathanaël Machicoane
Abstract : Among the large variety of materials fashioned for industrial needs, super-hydrophobic surfaces (SHS) have attracted increasing attention since the 90’s. Their physicochemical properties enable SHS to entrap a gas layer, referred to as plastron, in their roughness restricting thereby the solid-liquid contact area. This lubricating feature leads to liquid repellency, the so-called “Lotus effect”, which may strongly impact a wide range of engineering applications where wettability control is essential. Although extremely attractive for flow control purposes, SHS suffer from severe drawbacks limiting their performances in real-world applications. Among arising issues, the stability of the air-water interface is a cornerstone to warrant SHS efficiency and sustainability. This presentation is dedicated to the experimental investigation of the wake of free falling super-hydrophobic spheres within the so-called sub-critical regime. It is found that the air plastron adapts its shape to the flow-induced stresses, which compete with the surface tension. The study of the falling motion reveals that the plastron compliance has a sizeable influence on the wake development. Accordingly, taking into account the plastron deformation provides an attractive way to explain the somehow discordant results reported in other studies at comparable Reynolds numbers.
