Measurement Of Surface Flow Characteristics Of Puffer Fish And Its Bionic Drag Reduction Component

As one of the most popular drag reduction technologies,bionic surface drag reduction has the characteristics of low cost and no pollution.As a kind of migratory fish,the puffer fish has evolved a structure that can reduce the resistance it receives during migration during the long-term biological evolution.From this paper,the flow characteristics of the surface of the puffer fish and its bionic non-smooth drag reducing members are measured.The specific studies are as follows:(1)An underwater plane flow characteristic measuring device based on PIV technology is designed and built.According to the design requirements of the test platform and the requirements of the test sample,the measuring device is designed and built by combining the closed power driven circulating water hole with the PIV measurement technology.The test platform can be adjusted to meet the flow rate of 0.8~3m/s,and the test sample can be disassembled and replaced conveniently.The test section can satisfy that the flow field on the surface of the tested sample is turbulent.(2)The turbulent boundary layer on the skin surface of the center of the back and abdomen of puffer fish is measured at different inflow velocities by the measuring device.By comparing and analyzing the average velocity profile,turbulence intensity,Reynolds stress and vorticity,the drag reduction performance of the puffer fish epidermis is analyzed,and the drag reduction mechanism was explored.It is found that the epidermis of the puffer fish has a drag reduction effect compared to the smooth plate at a specific inflow velocity.The maximum drag reduction rate can reach 18.1%.The viscous bottom of the epidermis is thicker.The fluctuating velocity and Reynolds stress near the wall are smaller,but the vorticity is larger.(3)The epidermal morphology of different parts of the puffer fish is observed by field emission scanning electron microscopy and optical microscopy.The size,shape and arrangement of the scorpion spurs are obtained.According to the morphology and regularity,the thorn model is extracted and simplified.The bionic non-smooth components are measured,and the average flow characteristics are measured by the underwater plane flow characteristic measuring device.The velocity field,pulsation velocity and shear strain rate of the surface are analyzed and compared,and the variation law of the three is explored.The flow field structure characteristics of the bionic non-smooth component surface are obtained,and its drag reduction mechanism is explored.It is found that,within a certain range of variation,the longitudinal spacing of drag reduction elements only affects the normal velocity of the component surface,and the normal velocity decreases with its increase.The transverse spacing of drag reduction elements increases the thickness of boundary layer,the normal velocity and the pulsating velocity,but decreases the shear strain rate at the tip of drag reduction elements.Increasing the height of the drag reducing element will increase the thickness of the boundary layer,the normal velocity and the pulsation velocity.With the increase of velocity and fluctuating velocity,the shear strain rate at the tip of the drag reduction element first increases and then decreases,and the maximum height is about 3.75 mm.There is a low-speed flow field and a reverse vortex between the drag reducing elements,so that the original solid-liquid contact becomes liquid-liquid contact,and the drag reduction is realized.There are reverse vortices between high drag reduction elements,which can reduce the friction between low-speed flow field and high-speed flow field to achieve drag reduction.