Underwater drag reduction and gas film stability of superhydrophobic conical array surface under shear flow

Microstructured superhydrophobic surfaces represent an effective approach for drag reduction and reducing energy consumption of underwater vehicles. However, the gas film stability on microstructured surfaces remains insufficient, particularly under hydrodynamic shear conditions, which can lead to premature failure of drag reduction performance. Here, a superhydrophobic conically arrayed surface (CAS) is proposed to enable effective underwater drag reduction in Couette flow and enhance the stability of the gas-film by altering the cone structure. The gas-liquid two-phase-flow over CAS in a planar Couette flow configuration is investigated by COMSOL multiphysics. The key parameters, such as the cone height, inclination angle, and wettability, are analyzed to investigate their effects on the flow velocity, slip length, and drag reduction performance. The results demonstrate that the CAS induces a significant boundary slip velocity, effectively reducing hydrodynamic drag under laminar flow conditions. The slip length exhibits a positive correlation with the cone height, while drag reduction increases with an increase in the inclination angle. The inclined CAS configuration enhances the contact-line pinning effect, and thus further improves the gas-film stability under fluid shear conditions, enhancing sustained drag reduction. These findings provide a theoretical basis for designing and manufacturing functional drag reduction superhydrophobic surfaces for underwater applications.