Study On Manufacturing And Resistance Reduction Performance Of Aluminum Alloy Surface Gradient Hydrophobic Structure

In the current era of energy shortage,how to reduce the navigation resistance of Marine aircraft and reduce energy consumption has gradually become the focus of research in various countries.Drag reduction technology,as an important means to achieve energy saving and emission reduction,is a very competitive scientific research.A large number of experimental studies show that when the superhydrophobic surface is under water,a layer of air film will be sealed on the wall surface,resulting in flow and slip,which is a relatively efficient method of drag reduction.However,a large horizontal shear force will be generated at high water velocities.When the shear force is large enough,the gas film will be destroyed,resulting in a weakened drag reduction effect or even an increase in flow resistance due to the high surface roughness.Aiming at this problem of drag reduction failure,the hydrophilic and hydrophobic structure was constructed on the surface of aluminum alloy based on the method of combining laser and wire cutting to maintain the stability of the underwater surface gas film.The specific research contents are as follows:1)In order to produce surface with different wettability on aluminum alloy surface with high efficiency and large area,the aluminum alloy surface was directly crossed by laser after wire cutting,and the microstructure of the aluminum alloy surface was controlled by laser.After laser processing,the samples were divided into group A and group B for two kinds of follow-up treatment.Group A observed the change of surface wettability with time in the air after laser processing,while group B underwent low surface energy treatment after laser processing.2)Scanning electron microscopy(SEM),contact angle measuring instrument and other equipment were used to characterize the main properties of the sample surface,including surface microstructure,surface chemical element content after different parts were placed in the air,surface wettability change with time and static contact angle of different parts.Found in aluminum alloy surface after laser scanning rules combined with irregular shape of micro/nano structure,were treated with low surface energy of a surface can reach the super hydrophobic,maximum contact angle of 162.3 °,and in the air for the static contact angle on the surface of the sample will be increasing finally tends to be stable over time,the maximum contact angle of 154.6°.3)Based on the fluid calculation module in Comsol,the flow field characteristics of hydrophilic and hydrophobic models under different reynolds numbers were numerical simulated by setting the sliding wall in a two-dimensional model.The results show that the presence of bubbles will increase the near-wall velocity,but the bulge of bubbles will generate vortices at the hydrophilic and hydrophobic boundary.The more bubbles,the more vortices will be generated.Meanwhile,the different size and thickness of bubbles will have an impact on the flow field.4)Based on the differential pressure method,a drag reduction test rig was built to explore the drag reduction effect of various parts at different Reynolds numbers.It is found that the drag reduction rate of the sample increases first and then decreases with the increase of reynolds number,and finally becomes stable.When the drag reduction rate is stable,it is still higher than that of the full superhydrophobic aluminum alloy plate,indicating that there is still a very thin air film in the hydrophobic section of the hydrophobic phase sample,and the maximum drag reduction rate of the hydrophobic phase sample reaches 45.45% in laminar flow state.