Fish-inspired coating helps reduce drag on ship hulls

Polymer drag reduction is a method of reducing drag from fluid flowing through a confined area such as a pipeline or hose. Large polymers are added to the fluid and coat the inner surface, significantly reducing friction drag. However, this method is impractical for external flow applications such as on ships and submarines. A new approach is needed to apply this technique in this environment.

Xie et al. developed such an approach by taking inspiration from fast-swimming fish. The proposed design continuously releases polymer molecules from a coat applied to ship hulls.

Many fish secrete a polymer-based mucus from the microporous structure of their skin, giving them their characteristic slipperiness. The team used a similar concept to design composite coatings consisting primarily of gelatin and one of five rigid bio-polysaccharides: guar gum, xanthan gum, locust bean gum, tragacanth gum, and acacia gum. The microporous structure of the coating ensures the polymer is released in a controlled manner.

“The internal 3D net structures provided releasing access for the polysaccharide molecules,” said author Luo Xie. “Then, the drag-reducing polymer is slowly released at the coating slip surface under flow shear.”

In tests, each of the team’s coatings reduced drag by more than 20% when compared with a non-coated surface. They plan to further improve their design by tweaking the composition of their coatings.

“In the future, the effects of gelatin proportion and polysaccharide proportion would be further investigated to optimize the drag reduction performance of the coatings for different conditions,” said Xie.

Source: “Development and performance of a gelatin-based bio-polysaccharide drag reduction coating,” by Luo Xie, Lang Jiang, Fan-zhe Meng, Qiang Li, Jun Wen, and Hai-bao Hu, Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0149281 .

This paper is part of the Paint and Coating Physics Collection, learn more here .