Towards Drag Reduction in Turbulent Boundary Layers Using Dolphin-Skin-Inspired Compliant Surfaces

We aim to investigate the potential of dolphin-skin-inspired compliant materials for passive skin-friction drag reduction in turbulent boundary layers. The idea of using compliant materials to reduce skin-friction drag has a long history, which has led to numerous studies on their use for drag mitigation. However, results have often been inconsistent and the complex fluid–structure interactions involved are not well understood. Notably, dolphin skin is a natural anisotropic compliant material with distinctive structural patterns that are believed to play a key role in achieving drag reduction, however, there is no fast and reliable method to quantify the effects of the skin's specialized structural composition. To better quantify the effects of the anisotropic and layered nature of dolphin skin, we develop a resolvent-based modeling framework capable of capturing interactions between turbulent flow and realistic, finite-thickness, anisotropic compliant metasurfaces. This framework couples the linearized Navier–Stokes equations with a finite element representation of anisotropic solids, enabling efficient parametric studies of compliant surfaces. The model is validated against rigid-wall cases for both laminar and turbulent channel flows. We apply the method to two classes of materials: (i) isotropic compliant panels and (ii) anisotropic dolphin-skin-inspired panels with spanwise-periodic substructures. Results show how material stiffness, thickness, and anisotropy influence the amplification of turbulent flow structures, providing insights into the mechanisms of potential drag reduction. We discuss emerging design trends and identify optimal parameter regimes that enhance favorable fluid–structure interactions, laying the foundation for the development and deployment of practical passive drag-reduction technologies in both hydrodynamic and aerodynamic applications.