Dolphin-skin-inspired anisotropic flexible surfaces for turbulent drag reduction*

Skin-friction drag reduction (DR) in turbulent boundary layers (TBL) has significant economic and environmental benefits for both civil and military transportation. The study aims to investigate the potential of dolphin-skin-inspired compliant surfaces for achieving DR in TBLs. Dolphins, being among the most efficient swimmers in nature, have a skin that is a naturally anisotropic compliant material, which may offer valuable insights for designing optimal compliant surfaces for DR. Our framework integrates multi-disciplinary techniques to tackle this problem, including a resolvent-based model to determine optimal design parameters, fully coupled, high-fidelity, fluid-structure-interaction (FSI) simulations, and experimental tests using 3D-printed models and a water towing tank facility. We present an overview of our investigative framework and our progress towards the final goal, showing how all these different components are brought together to understand the causal relationships between different features of dolphin skin and drag reduction performance in high-Reynolds number flows. We further discuss the main modifications to near-wall turbulence over a compliant skin model that are associated with large skin-friction drag changes. Finally, we provide physical insights to design and manufacture optimal compliant surfaces for TBL DR.