Simulation and mechanism of the synergistic drag reduction performance of two types of microgroove surfaces and mucus

Wall friction resistance during underwater travel reduces propulsion efficiency and generates significant noise. While several drag reduction methods inspired by bionic principles have been proposed, they often fail to sustain high drag reduction over time. In this study, we optimize conventional rectangular grooves and design two new groove structures, with mucus secretion pores positioned below them. Rheological experiments on various drag-reducing agents reveal that the bionic mucus follows the Carreau model, and simulations identify the most effective mucus for drag reduction. A hydrodynamic model is developed to examine the synergistic effect of the drag-reducing grooves and bionic mucus, which is solved using large vortex simulations and analyzed accordingly. The results indicate that the highest drag reduction rate (37.5 %) is achieved when the mucus secretion velocity is 0.25 m/s in the curved groove. Using vortex dynamics theory, we propose a function that relates drag reduction rate to vortex volume for quantitative analysis. The theoretical calculations show a positive correlation between drag reduction and mucus secretion speed, consistent with the simulation results. We conclude that the drag reduction mechanism involves the combination of microgrooves and mucus, which reduces the number and density of vortex structures near the wall, slows their evolution, and weakens turbulence intensity, leading to drag reduction. By integrating simulation and theory, this study offers a reference for theoretical drag reduction calculations and presents new insights for designing drag-reducing surfaces.