Recent Developments of Superhydrophobic Surfaces (SHS) for Underwater Drag Reduction Opportunities and Challenges

Superhydrophobic surfaces (SHS) for underwater drag reduction draw more and more attention owing to its promising and wide applications such as underwater vehicles, pipeline oil transportation, and aquaculture. However, the drag reduction properties are inextricably linked to the stability of air layer on SHS. This review highlights recent advances regarding SHS for underwater drag reduction in the past three years. First, the fundamental theories are briefly described. Next, the crucial influencing factors, which include dimension and arrangement of particles, layout, and shape of the microstructures, Reynolds number, and attack angle on underwater drag reducing performance of SHS are thoroughly listed. Furthermore, the superior or inferior of these manufacturing techniques is also individually illustrated. After that, the solutions of enhancing stability of the air layer are explicitly classified. Then, the practical applications and its potential value in ships and underwater vehicles, microchannels, as well as fabrics are briefly discussed. Finally, the remaining challenges and promising breakthroughs in the field of SHS for underwater drag reduction are clarified in depth.