Research on the drag reduction property of puffer (Takifugu flavidus) spinal nonsmooth structure surface

Puffers show good drag reduction performance during migration. It is worth noting that spines which are different from ordinary fish scales are densely distributed on the puffer skin. Here, the special morphological structure of puffer spines was observed using microscopy techniques, accurate contour models were established based on image processing techniques and curve fitting, then feature sizes were obtained. Based on the results, the nonsmooth surface was established by orthogonal test to simulate the flow field. In addition, the influence of spinal structure on boundary layer flow field and the drag reduction property of nonsmooth surface were further analyzed. The nonsmooth surface formed by spinal structure elements can effectively reduce the wall shear stress and Reynolds stress, and there was a special "climbing vortex" phenomenon, so as to reduce the surface viscous friction resistance and achieve drag reduction. Compared with the smooth surface, the drag reduction rate of the nonsmooth surface was 12.94% when the inflow velocity was 5 m/s, which revealed and verified the drag reduction performance of the spines of puffer skin. The results lay a foundation for further research and optimization of drag reduction ability of nonsmooth surface of bionic spines. HIGHLIGHTS: The contour of the spinous process was accurately reflected by the Fourier function. The spines of puffer skin have good drag reduction effect. There was a special "climbing vortex" phenomenon to explain the drag reduction property.