Design,Fabrication Of Bionic Microstrctures And Study On The Drag Reduction Performance

With the improvement lever of people's living material,people's dependence on non-renewable resources has gradually increased.Therefore,improving energy efficiency has become a research hotspot.After long term natural selection,there are many organisms possession of drag reducion in nature.We find that there are a large n?mber of microstructures on their surfaces via research.The lotus leaf surface of microstructure with surface energy can capture air with high hydrophobicity,and the droplets are not wetting the surface,at the same time it has good drag reduction performance.The highly ordered riblets on shark surface can change the motion state of flow field and have good drag reduction performance.Through a large n?mber of experiments and theoretical studies,it is found that the microstructure of the biological surface has great research significance and application potential in reducing the resistance of the vehicle.In this paper,the fabrication and optimization of biological microstructures become the main topics,the effects of different microstructures on drag reduction performance are studied by experiment and simulation,in order to obtain the optimal microstructures,which possess of the maximize drag reduction ratio,at the same time,the drag reduction mechanism of different microstructures is explored,which provides theoretical support for the application of microstructures on actual navigation vehicles.Microstructure surfaces with different morphology are fabricated by chemical etching,anodic oxidation and sand blasting method.The results show that the embedded microstructures have good drag reduction performance by experiments and simulation.The maxim?m drag reduction ratio is 40% at flow velocity of 1.5 m/s,pore diameter of 100 nm,the eddy current is generated on the microstructure surface when the flow field flows through the embedded microstructure surface,which makes the friction resistance change into friction power and reduce the surface resistance.The prominent microstructures exhibit resistance increasing phenomena.The drag reduction rate decreases gradually along with the increase of flow velocity.The minim?m drag reduction ratio is-0.07%,at the roughness 4.7 ?m and the velocity of flow 1.5 m/s,the drag reduction ratio decreases,because produce the form pressure among the prominent microstructures when the flow through the prominent microstructures surface.We fabricate superhydrophobic surface for above the structure by low surface energy modification.Which can entrap a large amount of air on the hydrophobic surface.It is found that the droplets on the hydrophobic surface roll on the superhydrophobic surface.Because of the surface tension of the droplets,the droplets move in the form of separation and contact with the surface,thus taking away the impurities on the hydrophobic surface.We find that the drag reduction rate of superhydrophobic surface decreases with the increase of flow velocity by water tunnel experment and simulation study.The entrapped air by superhydrophobic surface gradually escapes with the increase of flow velocity,and reduces the contact area between gas and liquid,which reduces the slip velocity and length of flow field.At the same time,the microstructure enlarges the contact area between the solid and liquid,the wall friction resistance increases after the entrapped air escapes.The maxim?m drag reduction ratio is 19.2 % when the velocity of flow is 0.5 m/s.Duing to the difficulty of fabrication and the entrapped air instable among the surperhydrophobic surface,we investigate drag reduction performence of the difference morphology of microstructure by simulation.We find that the morphology of microstructure affected the micro-vortex generation and have an important influence on the size,shape and location of micro-vortex.The size,shape and location of microvortex directly affected the value of the form pressure between the front and back walls among of microstructure.The morphology of microstructure on drag reduction performance is studied by the interaction of pressure difference resistance and wall friction resistance.The results show that the drag reduction performance of hyperbolic manifold microstructure is superior to the simple manifold microstructures,the simple manifold manifold microstructure is superior to the rectangular,the rectangular is superior to the semi-circular,the semi-circular is superior to the triangular,and the maxim?m drag reduction ratio is 2.16% at the velocity 2 m/s.