Study On Drag Reduction Characteristics Of P.Dabryanus Loach Surface Flexible Micro-morphology

Because the working parts of paddy field machinery are often in contact with muddy water,the working parts are subject to huge resistance,which is easy to cause serious wear and tear.Meanwhile,it also causes energy waste and reduces working efficiency.Therefore,it is of great significance to study the drag reduction of working parts of paddy field machinery.Loach lived in mud for thousands of years,and its living environment was very similar to the working environment of paddy machinery.In order to adapt to the law of natural selection,the surface of loach developed the drag reduction function under the condition of muddy water.The drag reduction function is not only derived from mucus,but also the surface microscopic appearance and the flexible skin play an important role in the drag reduction function.At the same time,surface microscopic appearance plays an important role in the adsorption and maintenance of mucus.In this paper,loach skin was taken as the bionic prototype and fluid-solid coupling simulation analysis method was used to analyze its drag reduction characteristics and optimize its surface structure.Samples of flexible bionic structure were designed and carried out drag reduction tests.The main research contents and conclusions of this paper are as follows:(1)Analysis of surface micromorphology and flexibility characteristics of loach.The scales of the loach were observed with 3D hyperfocal distance microscope and scanning electron microscope(SEM).The results showed that the scales of the loach were elliptic in general and could be divided into four parts: the basal area,the lateral area,the top area and the scale focal area.Among them,the groove structure of loach in the top of scales was most uniformly distributed.The skin samples of loach were analyzed by tensile test,The elastic modulus of loach skin was 2.47-9.13 Mpa,and the average elastic modulus of loach skin was7.03 MPa,and Polydimethylsiloxane(PDMS)was selected as the bionic sample material.(2)Drag reduction performance analysis.Taking part of the groove structure in the loach's scaly top area as the prototype,using Soildworks software established a 3D model,and the groove was analyzed by two-way fluid-structure coupling by ANSYS Workbench software.The results show that when the fluid flows through the surface,the deformation of the flexible trench will change the flow field distribution in real time and form a low-speed vortex water-trapping region near the wall surface,thus reducing the contact area between the fluid and the solid region and reducing drag to a certain extent.The simulation results show that the flexible loach groove structure has the best drag reduction effect at 1m/s,with a drag reduction rate of 2.57%,under the flow rate of water medium of 1-10m/s.(3)The optimal parameter combination of the groove microstructure model was optimized by single factor test and orthogonal test,when the height of the groove ridge was5?m,the width of the groove ridge was 2?m,the distance between adjacent ridge was 4?m,and the biomimetic material elastic modulus was 2.678 MPa,the maximum drag reduction ratecould reach 2.25% in the aqueous medium at 1m/s.(4)Trial manufacture and resistance reduction test of bionic resistance reduction samples.A silicon wafer with the appearance of loach was fabricated by photoligraphy,and the loach skin flexible groove structure was processed by vacuum silica gel embossing on the solidified PDMS material surface.Design and build the water tunnel test rig for bionic sample drag reduction performance verification test.The experimental results show that the biomimetic flexible structure sample has a certain drag reduction effect in the water medium,and the resistance increases with the increase of the incoming flow velocity,but the resistance of the biomimetic flexible structure sample is less than that of the smooth plane at the same velocity.The maximum drag reduction rate of the bionic sample was3.07%.In this study,loach which is good at swimming in mud,was used as the bionic prototype to analyze the drag reduction characteristics of the flexible surface with microscopic morphology,and the bionic drag reduction samples were designed and processed,laying a preliminary foundation for the drag reduction research of paddy field machinery,and even other overwater and underwater vehicles.