Investigation into the Hydrodynamic Drag Reduction Mechanism of Eel Skin Mucus

To address the challenge of solid-liquid interface frictional resistance, this study systematically investigated the hydrodynamic drag reduction mechanism of eel skin. The tribological properties were quantitatively evaluated and comprehensively analyzed using a friction and wear testing machine, a rotational rheometer, and an interface resistance measurement device in a circulating water tunnel. Results demonstrated that the compact layered structure of the eel's epidermis significantly enhanced its mechanical strength, thereby providing a robust physical foundation for mucus secretion by the mucus cells beneath the epidermis. Moreover, the abundant fat and protein beneath the skin formed an elastic network that not only improved the overall structural stability but also enabled the eel to adapt dynamically to complex flow fields in marine environments. The mucus secreted by the eel's epidermis was a highly hydrated biomacromolecule with multifunctional properties, including reducing friction during predator evasion, minimizing swimming resistance, and facilitating adaptation to aquatic environments. Additionally, this mucus had a lubricating effect and could form a stable hydrated layer on the surface. When the shear frequency exceeded the critical value, shear thickening occurred. Under the thickened state, the epidermal mucus of the eel worked in concert with the deformation of the eel's epidermis to absorb impact energy, suppressing the formation of turbulence, further stabilizing the barrier state of the hydrated layer, and thus maintaining the drag-reducing effect.