Progress and Future Challenges in Bionic Drag Reduction Research Inspired by Fish Skin Properties.

During the long course of evolution, fish have developed complex skin structures to adapt to the dynamic aquatic environment. These skin features not only reflect optimal adaptation to the aquatic environment but also play a key role in effectively reducing fluid drag and improving swimming efficiency, to reveal the intrinsic connection between the complex skin structure of fish and drag reduction performance and to provide new design ideas for the drag reduction surface of underwater vehicles. Based on the different drag reduction characteristics of fish skin structures, this paper divides existing biomimetic drag reduction technologies into three categories: riblet drag reduction, flexible drag reduction, and composite drag reduction. In terms of biomimetic riblet drag reduction, the drag reduction characteristics of shark skin and its biomimetic application were analyzed and the drag reduction mechanism of riblet structures affecting flow characteristics was revealed. Focusing on the flexible skin of dolphins, which differs from the rigid riblet structure of sharks, we further analyzed the role of flexible skin in reducing drag and maintaining high-speed movement. The different effects of flexible skin and riblet skin on flow characteristics were compared, and the mechanism and effect of flexible drag reduction were revealed. In addition, the mechanism of the synergistic effect of composite factors on flow characteristics and drag reduction effects was analyzed for the skins of other fish species. Finally, the challenges faced by bionic drag reduction technologies prototyped from fish species are summarized and future research directions and priorities are outlined.