Computational investigations of bubble growth on super-hydrophobic surfaces

In this computational work, we studied bubble growth on super-hydrophobic surfaces (SHSs) using Basilisk, an open-source multiphase flow solver that adopts a finite-volume approach for solving the Navier-Stokes equations and the Volume-of-Fluid method with adaptive mesh refinement for capturing the gas-liquid interface. The SHS was modelled as a smooth surface with a prescribed static contact angle. The bubble was formed by injecting air through an orifice at a constant flow rate. Our results successfully captured the trends observed in the experiments, which showed an increase of detached bubble volume with increasing gas flow rate, size of super-hydrophobic region, and static contact angle in quasi-static regime. The bubble shape and detached volume had excellent agreement with the experiments. Furthermore, complementing the experiments, the simulations resolved the pressure and velocity distributions within the bubble, elucidating the mechanisms of bubble growth and detachment. Lastly, complex problems of bubble growth in dynamic regime and multi-bubble growth through multi-orifice were investigated. The results of this study can assist the implementation of bubble injection as an effective technique to sustain the Cassie-Baxter state and drag reduction property of SHS.