Prediction the variation of shark scale's attack angles in swimming

Abstract

Shark is the fast swimming animal in the ocean, and it is well-known for sharkskin effect. Sharkskin is covered by the tiny and rigid scales, which can stick out of the viscous sublayer and effectively inhibit the occurrence of turbulence and reduce the wall resistance. The longitudinal sections of the scale surface are not parallel to the flowing direction, but at a particular attack angle, which could be considered as a supplement to the mechanism of sharkskin effect. At present, it is almost impossible to observe the variation of scales’ attack angles during the biological shark's swimming. Although the real sharkskin surfaces with original sizes have been fabricated by the bio-replicated method, the attack angles cannot be exactly controlled, the result of which is that the drag-reducing efficiency of sharkskin with different attack angles cannot be obtained by the experimental methods. In this paper, the highly accurate three dimensional digital model is exactly built through the high-accurate scanning the biological sharkskin, and the micro flow field is investigated comprehensively and deeply, especially that, the influence of scales’ attack angles on drag-reducing efficiency is analyzed, which has the important significance on exploring the sharkskin effect.