Fish-scales inspired multilevel micro-nano structures for water drag reduction on metal surface

Abstract Bionic drag-reducing surfaces are promising for marine transportation and underwater diving due to their good drag-reducing properties. There are more studies on the single macrostructure and single microstructure of bionic fish scales, and few studies have been conducted to combine the macrostructure and microstructure of fish scales. In addition, most researchers have over-simplified the extraction of bionic templates and have not achieved a refined configuration of fish scales. In this study, by combining the macro-structure of fish scales with the micro-structure of the posterior region and proposing a unique laser path scanning strategy, the refined conformation of the 3D structure of bionic fish-scales at different depths and simple large-area preparation are realized by the unique processing modes of different numbers of etching lines and the superposition of different etching laser paths. In addition, we conducted drag reduction tests on the samples. The results show that the bionic fish scale composite structure has a significant drag reduction effect. When the Reynolds number is 750, the number of microstructures on the bionic fish scale is 6, and the transverse spacing is 120 μm, the bionic carp scale composite structure has the maximum drag reduction of 36.17%. This research is of great significance to the research of drag reduction in navigation and transportation, engineering machinery and underwater equipment.