Current drag reduction research predominantly focuses on micro-scale surface modifications inspired by sharkskin or riblet textures, often overlooking the synergistic effect of macro- and micro-scale structures. This study proposes a cross-scale biomimetic fish scale array structure designed based on fluid-structure interaction principles. A three-dimensional laminar flow simulation using COMSOL Multiphysics was conducted to evaluate the drag reduction performance. The model incorporates a tiled array of fan-shaped fish scales with embedded parallel microchannels, simulating gas-liquid-solid interaction in a low-speed water environment. A systematic parametric optimization was performed, involving aspect ratio, edge curvature radius, microchannel depth and spacing, edge height, and gas fraction. The optimal configuration—aspect ratio of 150 %, curvature radius of 150 mm, microchannel period of 0.2 mm, duty cycle of 80 %, and semi-circular cross-section—achieved up to 20 % reduction in drag compared to a smooth surface under 2 m/s laminar flow. Further simulations show that drag reduction decreases with increasing immersion depth but stabilizes around 20 % beyond 10 m. Flow visualization revealed that clockwise vortices form in the posterior edge of the fish scale, modifying the boundary layer and promoting slip flow, acting similarly to rolling bearings that reduce surface friction. Moreover, directional flow tests demonstrated that forward flow along the scale arrangement results in significantly higher drag reduction than perpendicular or reverse directions. These findings indicate that combining macro-scale geometry with microchannel-induced slip flow can effectively reduce resistance and promote energy efficiency in underwater applications. The study introduces an effective, scalable drag-reducing surface that bridges microstructure benefits with macro-scale flow-altering geometry, offering a novel approach for the design of energy-saving marine coatings and pipeline linings.
Chen et al. (Thu,) studied this question.