Stability and drag reduction mechanism of mucus-water interface on underwater vehicle surface

To research the drag reduction performance and mechanism of the mucus–water interface from the perspective of the stability of the liquid–liquid interface, based on the research method of the horizontal collector interface and the basic theory of microchannel two-phase flow, the mechanical parameters such as viscous force, interfacial tension, and shear force, as well as physical parameters such as the water flow rate, mucus discharge rate, mucus discharge aperture, and mucus properties on the stability of the mucus–water interface were investigated using the computational fluid dynamics software and the designed and constructed test rig for the analysis of the stability of the microscopic interface. The research examines how physical parameters like water flow rate, mucus discharge rate, mucus pore diameter, and mucus properties affect the stability of the mucus–water interface. A test bench was constructed to evaluate how water flow and mucus discharge rate influence drag reduction performance. Results show that the interface is most stable when the water flow rate is 0.1 m/s, the mucus discharge rate is 0.05 m/s, the mucus pore diameter is 0.16 mm, and interfacial tension is 0.08 mN/m, leading to the longest slip length. Increasing mucus discharge velocity, and pore diameter, and using mucus with higher interfacial tension enhances interface stability and increases slip length. The drag reduction mechanism occurs because an increase in slip length reduces the velocity gradient near the surface, which in turn decreases the shear stress in the turbulent boundary layer, enhancing the drag reduction effect. Additionally, mucus with higher dynamic viscosity helps form a uniform layer, improving interface stability and reducing friction from instability. However, it also increases shear force at the mucus–water interface, which may counteract the drag reduction effect.