Investigation on Drag Reduction Mechanism of Biomimetic Functional Surface Cylinders in Dynamic Volume and Pressure Conditions

ABSTRACT Inspired by the drople dynamics drag reduction properties of dragonfly wing surfaces, the biomimetic drag‐reducing functional surface cylinders are prepared. Their drag reduction performance and the mechanism of bubble‐induced drag reduction under dynamic volume and pressure conditions were studied. The influence of key factors such as texture types and coating categories on drag reduction performance is systematically analysed by a constant‐volume variable‐pressure interstitial flow system (single‐channel) and a recirculating variable‐volume experimental system (dual‐channel). The experimental results show that all shapes of cylindrical biomimetic textured surfaces have air bubbles aggregated in the textured cavities when falling. The air bubbles reduce the friction at the solid–liquid interface and have an obvious drag reduction effect, with the square texture having the best effect. Furthermore, the hydrophobic state surface cylinders under the composite treatment of coating and texture have the largest drag reduction rate of 18.7%. Based on the theoretical model of two‐phase flow, the mechanism of drag reduction by low‐speed vortex flow has been investigated through numerical simulation of liquid interstitial flow characteristics on the textured surface. The results demonstrate that the low‐speed vortices present inside the texture interact with the high‐speed water flow outside the texture; the frictional resistance at the solid–liquid interface is effectively reduced. The shear stress on the cylindrical surface is significantly suppressed by the texture.