Loach-inspired V-microgrooves coupled with microbubbles for stable gas film and enhanced underwater drag reduction

Frictional drag significantly increases energy consumption in underwater vehicles. Inspired by loach scales, we designed a biomimetic drag reduction surface integrating V-shaped microgrooves and microbubbles. Numerical simulations based on the population balance model (PBM) in fluent revealed that bubble diameter and volume fraction are critical factors, achieving maximum drag reduction efficiencies of 29.1% at a bubble diameter of 50 nm and 30.2% at a 1.2% volume fraction, with pressure drag reduction as the dominant contributor. A flexible superhydrophobic surface was fabricated via vacuum demolding and thermal treatment, exhibiting a static contact angle of 157° and stable gas-film formation. Flow-channel experiments demonstrated a drag reduction efficiency (DRE) of 30.92% at 4.43 m s^-1. These findings reveal the cooperative effect of surface microstructures and microbubbles in sustaining the air-water interface, providing a feasible strategy for high-efficiency underwater drag reduction in practical applications.