Hydrodynamic performance modulation via flow transition triggered by biomimetic leading-edge protuberances

Leading-edge protuberances, inspired by humpback whale flippers, have emerged as a promising passive flow control strategy for marine lifting surfaces. However, their influence on flow dynamics and transition processes under realistic operating conditions remains insufficiently understood. This study presents a biomimetic modification of a NACA66 hydrofoil and systematically investigates the transitional-to-turbulent flow mechanisms and associated energy characteristics. Large eddy simulations (LES) are conducted over a range of angles of attack (6°-14°) and chord-based Reynolds numbers (0.75×10 6 -1.5 × 10 6 ). Dimensional analysis is adopted to identify key dimensionless parameters governing hydrofoil hydrodynamic behavior, providing supporting inputs for subsequent performance analysis. The results show that the biomimetic hydrofoil significantly delays stall onset by approximately 18-22% and enhances operational robustness at elevated angles of attack, although a considerable reduction in peak lift-to-drag ratio is observed, this trade-off yields improved stall resistance and operational robustness under high-angle-of-attack conditions. Mechanistically, the leading-edge protuberances induce streamwise counter-rotating vortex pairs that reorganize the near-wall flow structure. These vortices generate localized upwash in trough regions, effectively increasing the local angle of attack and promoting early but controlled transition. The resulting partial flow separation contributes to lift augmentation while simultaneously increasing drag. Furthermore, flow reflection within trough geometries enhances wall-normal momentum transport, accelerates boundary layer transition, and suppresses low-frequency pressure fluctuations associated with instability. Overall, the biomimetic design modifies the energy redistribution process from transition to turbulence, trading peak efficiency for enhanced flow stability and maneuvering adaptability. These findings provide new insights into the hydrodynamic role of bio-inspired surface morphologies and offer guidance for the design of high-performance underwater lifting devices.