Research On Manufacturing Of Bionic Fish-scale Microstructure And Drag Reduction

With the development of marine transportation and underwater navigation technology,the fluid drag reduction,as an important technology to save energy and reduce environmental pollution,has become an international research hotspot.Many scholars have studied aquatic organisms on the basis of bionics,and the results showed that the body surface structure of many organisms had unique drag reduction performance.Therefore,it is a feasible and significant research direction to replicate the morphological features of the biological body surface on the surface of the material.How to optimize and manufacture the bionic surface on a large scale and at low cost is the research focus of bionic drag reduction technology.In this study,a high efficiency,low cost,clean and environmentally friendly processing method was proposed.Based on the morphological characteristics of fish scales,the bionic fish-scale surfaces were prepared by laser etching on the surfaces of aluminum alloy.The research contents and conclusions of this paper can be summarized as follows:1)By observing the arrangement and morphological characteristics of fish scales,the biological prototype of bionic fish scales was summarized and extracted.The arrangement and morphological characteristics of fish scales were abstracted into oblique-grooves structure,and a three-dimensional model of bionic fish-scale with pit structure was constructed.The laser etching path was designed based on the three-dimensional model.Different forms of bionic fish-scale structure were prepared on smooth aluminum alloy surface by optical fiber laser device.Ultra-depth electron microscope,laser confocal scanning microscope and scanning electron microscope were used to characterize the microscopic morphology and the element composition of the bionic fish-scale surface.2)COMSOL software was used to study the characteristics of the flow field on the surface of bionic fish-scale.Through the method of numerical simulation,the single factor experiments and orthogonal experiments of four factors were studied,including the angle of fish-scale,the depth of grooves,the arrangement distance and the velocity of the water flow.The optimal combination of these factors was obtained: the fish-scale angles is 120°,the depth of groove is 130?m,the arrangement distance is 2300?m,and the flow velocity is0.4m/s.The theoretical drag reduction rate of this combination is 7.8460%.Through numerical simulation analysis and comparison of the flow field characteristics of each surface,it was found that all the bionic surfaces had obvious low resistance zones.Compared with the smooth surface under the same water flow velocity,the average viscous stress of the bionic surfaces was smaller,which showed the obvious drag reduction effect.In addition,an“secondary flow” vortex was generated in the bionic fish-scale grooves.3)Based on the principle of pressure differential resistance test,a fluid drag reduction test device was built.The whole test equipment includes three parts: inlet drive,flow control and pressure test.According to the designed orthogonal experiment,the bionic fish-scale samples were prepared.The drag reduction performance of all samples was tested,and the drag reduction rate of the samples was analyzed.The results showed that the surface of the bionic fish-scale had the effect of reducing drag,and the measured maximum drag reduction rate was 8.2745%.Based on the analysis of flow field characteristics by numerical simulation,the drag-reducing mechanism of bionic fish-scale surface was explained combined with the current grooves drag reduction technology.The vortex structure generated in the fish-scale grooves acts as a “fluid-rolling bearing”,which effectively reduces the viscous stress on the wall surface.Compared with the common transverse grooves,the bionic fish-scale surface has an obvious advantage in drag reduction technology.