Fabrication and Drag Reduction Performance of Bionic Surfaces Featuring Staggered Shield Scale Structures.

To investigate the drag reduction mechanism of shark skin placoid scales and develop high-efficiency drag-reducing surfaces, this study designed and fabricated a biomimetic shark skin surface featuring staggered microscale groove structures. The fabrication process involved laser etching on silicon wafers to create a placoid microstructure template, followed by polydimethylsiloxane (PDMS) replication to obtain biomimetic shark skin samples. Sedimentation experiments demonstrated that the biomimetic surface significantly reduced settling time compared to a smooth surface, achieving a drag reduction rate of 5.65%. Further computational fluid dynamics (CFD) simulations were conducted to analyze the near-wall flow characteristics around the biomimetic surface. The results revealed that the drag reduction mechanism primarily stems from the effective regulation of near-wall laminar flow by the micro-groove structures: a low-velocity fluid layer formed within the grooves reduces the near-wall velocity gradient, thereby decreasing frictional drag, while stable recirculation zones develop within the grooves, contributing to momentum redistribution and reduced energy dissipation. Additionally, the staggered arrangement of the grooves promotes a smoother pressure distribution along the flow direction, mitigating pressure drag by reducing the pressure differential between windward and leeward surfaces. The experimental and simulation results showed excellent agreement (simulated drag reduction rate: 5.08%), collectively verifying the feasibility and effectiveness of the proposed biomimetic placoid structure in achieving fluid drag reduction.