Bionic research on Paramisgurnus dabryanus scales for drag reduction

Abstract

Drag reduction is a key problem in marine vehicles and fluid transportation industries. Reducing drag strategies and mechanisms need to be further investigated. To explore a bionic approach for reducing flow resistance, experimental and numerical simulation research was conducted to study the drag reduction characteristics of the Paramisgurnus dabryanus surface microstructure. In this study, the large-area flexible surface of the bionic loach scale was prepared by the template method of one-step demoulding. The water tunnel experiment results show that compared with the smooth surface, the drag reduction rate of the bionic surface ranges from 9.42% to 17.25%. And the numerical simulation results indicate that the pressure gradient and low-speed vortex effect created by the bionic loach scales can effectively reduce the friction drag. The results of experimental data and numerical simulation both prove that the bionic scales of Paramisgurnus dabryanus can achieve the underwater drag reduction function. This research provides a reference for drag reduction in marine industries and fluid delivery applications.

Fig. 1. Morphological observation of loach scales. (a) P. Dabryanus loach. (b) Scale beneath the skin. (c) Different regions on a single scale. (d) Size and arrangement of scales. (e) Thickness of a scale.

Fig. 2. Bionic scale 3D visualization model.

Fig. 3. Preparation process of bionic scales. (a) CNC precision machining. (b) PDMS die casting. (c) Flexible bionic surface.

Fig. 4. Anti-structure surface. (a) Dimensions and overall distribution. (b) 3D image of topography. (c) 3D image of anti-structure.

Fig. 5. The bionic sample. (a) Rigid anti-structure and flexible PDMS structure. (b) Dimensions and overall distribution of flexible PDMS surface. (c) 3D topographies image.

Fig. 6. Water tunnel experiment bench.

Fig. 7. Computational domain model.

Fig. 8. Results of water tunnel experiment. (a) Friction factor distribution. (b) Drag reduction rate at different Reynolds numbers.

Fig. 9. Surface wettability. (a) The contact angle of the smooth surface. (b) The contact angle of the bionic surface.

Fig. 10. Resistance simulation results. (a) Total resistance distribution; (b) drag reduction rate distribution.

Fig. 11. Distributions of pressure and velocity. (a) Near-wall pressure contour. (b) Velocity vector diagram. (c) Bionic surface velocity contour. (d) Smooth surface velocity contour.

Fig. 12. Flow field variation. (a) The pressure distribution curves of line ST and BT. (b) Velocity distribution curves of line SO and BO. (c) Turbulent kinetic energy distribution curves of line SL and BL. (d) Wall shear stress distribution curves of line SO and BO.