Active Gas-Supplied Superhydrophobic Porous Grooved Interfaces for Broadening the Effective Range of Underwater Grooved Drag Reduction

Abstract Reducing underwater drag is important for improving the endurance and energy efficiency of marine equipment. Grooved surfaces and superhydrophobic coatings hold promise for drag reduction; however, conventional grooves require scale matching with near-wall turbulent structures, whereas passive superhydrophobic surfaces suffer from air film depletion under high-speed flow. In this study, an active gas-supplied superhydrophobic porous grooved interface is proposed for drag reduction. The interface consists of a selective laser-melted, three-dimensionally interconnected porous steel substrate, grooves, and a superhydrophobic coating. The porous substrate acts as an internal gas transport and distribution layer, and streamwise grooves confine the supplied air film. The active gas supply reconstructs the gas–liquid interface inside the grooves, shifts the near-wall velocity profile upward, suppresses near-wall vorticity, and reduces wall shear stress. At Re = 74000, the optimized surface achieved a maximum drag reduction rate of 31.9% under a regulated gas supply. By coupling active air film replenishment with groove confinement, this strategy reduces the dependence of grooved surfaces on strict scale matching and extends the effective operating range. Furthermore, a piezo-air pump with a high-pressure load capability was introduced as a self-supplied gas source, enabling localized gas compensation at Re = 46000. This study provides an active air-film regulation strategy for miniaturized drag reduction applications in marine equipment.