Optimization of bionic microgroove surface and its synergistic drag reduction performance with mucilage

The frictional resistance induced by turbulent boundary layers on the surfaces of underwater vehicles, such as ships and submarines, constitutes a substantial proportion of their total drag, presenting a major impediment to energy efficiency and operational performance. Inspired by the synergistic drag-reduction mechanisms found in marine organisms—for instance, the microgroove structures on shark skin in conjunction with surface mucus—this study explores the collaborative effect of biomimetic microgrooves and synthetic mucus on drag reduction. Currently, research on the combined application of surface microgrooves and mucus-like substances for drag mitigation remains scarce. In this work, quasi-periodically arranged spanwise grooves and discontinuous streamwise grooves were designed, with an aqueous mPEG solution employed as a biomimetic mucus substitute. A hydrodynamic model was developed to analyze flow characteristics within the boundary layer and coherent structures through numerical simulations, thereby elucidating the underlying mechanisms of drag reduction. Experimental studies were conducted to validate the simulation results. The findings demonstrate that as the mucus secretion rate increases, the near-wall turbulence intensity, peak Reynolds stress, number of velocity streaks, and density of streamwise vortices all decrease. Maximum drag reduction rates reached 21.53% in simulations and 21.08% in experiments.