Research progress of slippage characteristic and gas film stability enhancement methods on biomimetic hydrophobic surfaces

The biomimetic hydrophobic surface is a potentially efficient underwater drag reduction method and the drag reduction mechanism of this kind of surface comes from the interfacial slippage. For now, it is a hotspot to grasp the slippage characteristic and explore slippage enhancement strategies. This paper not only summarizes our numerical simulation and experimental results of slippage characteristic at the solid-liquid interface (SLI) of hydrophobic surfaces (HS) and the gas-liquid interface (GLI) of superhydrophobic surfaces (SHS) in recent years, but also introduces some innovative methods that can effectively improve the gas film stability and drag reduction effect of SHS. First, we used the molecular dynamics (MD) simulation method to figure out the effect of the solid-liquid interaction strength, the system temperature and the shear rate on the slippage of SLI, and expound their action mechanism from molecular scale. Then, by MD and multibody dissipative particle dynamics (MDPD) method, the slippage behavior at the GLI was studied under the influence of the microstructure size and the flow driving velocity. We proposed a new kind of hybrid slip boundary condition model to describe the slippage characteristic on GLI. In addition, we found through experiment that a three-dimensional backflow will appear on the GLI under the interfacial adsorption of surfactants, and the backflow direction will reverse with the change of GLI morphology. Finally, we put forward the wettability step structure and gas injection method to enhance the stability and drag reduction effect of the gas film on SHS.