Hydrodynamic performance enhancements of shark skin-inspired surfaces on foils and robotic fish fins*

Enhancements to improve the hydrodynamic performance of unpiloted underwater vehicles (UUVs) are crucial for next-generation designs, with applications in nearshore and ocean monitoring. One approach is to mimic advantageous biological features, such as shark skins for turbulent drag reduction and fish fins for maneuverability. In particular, sharks have dermal denticles, or microstructures that decrease skin friction. Bioinspired designs using rigid denticles on rigid or compliant surfaces have demonstrated increased lift-to-drag ratios at low angles of attack in laminar flow, but have not yet been tested experimentally at higher Reynolds numbers, or used compliant denticles. To address these open questions, we manufactured denticle panels using stereolithography, collected hydrofoil force measurements in a recirculating water tunnel with flow speeds up to 3.5 m/s, and validated preliminary results of a 3D unsteady Navier-Stokes solver. Denticles were then applied to robotic fish fins to test the combined effect of multiple bioinspired features on swimming performance. Future work will focus on improving the speed, energy efficiency, and antifouling properties of UUVs to enhance persistence and minimize vehicular noise signatures.