Effective Underwater Drag Reduction: A Butterfly Wing Scale-Inspired Superhydrophobic Surface

Abstract

The microstructured superhydrophobic surface serves as an alternative strategy to decrease resistance of underwater vehicles, but the sustainment of an entrapped air layer and the stability of the corresponding gas−liquid interface within textures in flow shear or high pressure are still a great challenge. Inspired by the scales of Parantica melaneus wings, we propose a biomimetic surface with a hierarchical structure featuring longitudinal ridges and regular cavities that firmly pin the gas−liquid interface. The drag reduction rate of the Butterfly Wing Scale-Like Surface (BWSLS) demonstrates a noticeable rise over the single-scale textured mainstream biomimetic surfaces at moderate Reynolds numbers. The superior drag reduction mechanism is revealed as the synergistic effect of a thicker gas film and a more pronounced secondary vortex within the hierarchical textures. The former reduces the velocity gradient near the surface, while the latter decreases the vorticity and energy dissipation. In a high hydrostatic pressure environment, the proposed surface also demonstrates significant stability of the gas−liquid interface, with a gas coverage rate of over 67% during the cyclic loading, surpassing single-structured surfaces. Our study suggests promising surface designs for optimal drag reduction by mimicking and leveraging diverse surfaces of organisms adapted to oceanic climates.

Self-Driven Gas Spreading on Mesh Surfaces for Regeneration of Underwater Superhydrophobicity

“…The aquatic plant Salvinia preserves the plastron for a long duration by pinning the water–air interface by the hydrophilic tips on its hydrophobic leaves . Due to the hydrophobic property and micro/nanostructures on the surface, these superhydrophobic surfaces are capable of trapping a plastron, which has garnered significant attention due to their potential applications in various nonwetting-related fields, including drag reduction, − antifouling, − wearable devices, − collection, and anti-icing. − …”