Preparation And Drag Reduction Mechanism Of Micro-Nano Bionic Superhydrophobics In Flowing Blades

Inspired by superhydrophobic plants in nature,the wettability and surface microstructures of plants were explored.The surface structures were extracted and optimized by CFD numerical simulation.The stable superhydrophobic bionic samples were obtained by high-speed WEDM,which provided theoretical basis for fluid machinery and fluid transportation.In this paper,four kinds of plants,Canna leaf,Canna flower,Setaria and Clover,were selected to study and test.It was found that the leaves of Canna,Setaria and Clover exhibited good superhydrophobicity.The surface structure of Canna is a regular network structure,and the surface is covered with a convex-package structure.Nano-sized particles are attached to the network structure to form micro-nano composite structure,which is an important factor affecting the superhydrophobic performance.The structure surface of Setaria and Canna was striped,while that of Setaria showed long stripes,but the stripe spacing was not uniform.The surface of Canna was discontinuous stripes,but the stripe spacing was basically the same.The surface structure of superhydrophobic plants provides a theoretical basis for the study of biomimetic superhydrophobic samples,and provides an important research basis for the subsequent application of superhydrophobic surfaces to fluid mechanics and fluid transportation.The process of droplet impinging on superhydrophobic surface was simulated by CFD.The surface structure of the three plants was optimized into convex hull structure and stripe structure,and the mathematical model was established.The grids were divided by ICEM pretreatment software.The VOF calculation method was introduced into FLUENT software to track the flow characteristics of solid-liquid interface.The convex hull and stripe structures optimized by CFD simulation have good superhydrophobic properties,and the droplets exhibit low adhesion on the rising surface.CFD numerical simulation provides an effective simulation method for thestudy of superhydrophobic surface.The superhydrophobic structure can be optimized by numerical simulation.The optimized structure can be machined and carved onto the metal surface,and the superhydrophobic surface can be successfully applied to the actual production and life fields.After the effective extraction and analysis of superhydrophobic microstructures,the superhydrophobic microstructures were etched onto the surface of aluminum alloy by high-speed WEDM to construct the bionic superhydrophobic samples.Five groups of bionic samples with convex hull structure and stripe structure were constructed respectively,and the surface morphology,contact angle,contact time and chemical composition of bionic samples were analyzed by scanning electron microscopy,contact angle measuring instrument,high-speed camera platform and infrared spectroscopy.The results showed that the bionic samples have good superhydrophobicity,and the contact angle is between 150 degree and 160 degree,the contact time is between 10 ms and 15 ms.In addition to extracting and optimizing micron-scale convex hull structure and stripe structure,the surface of bionic samples is covered with micron-scale structure composed of alumina debris.The two structures constitute micro-nano composite structure,which is the main factor affecting superhydrophobicity.Compared with the droplet morphology changes on the surface of the bionic sample and smooth sample,the droplet can be ejected smoothly from the surface of the bionic sample due to its low adhesion,but the droplet on the surface of the smooth sample can only adhere to the surface of the sample due to its large viscous force.Compared with the bionic sample experiment and the numerical simulation analysis,the error of droplet spreading coefficient between the numerical simulation and the bionic sample experiment is generally less than 5%,there is a certain deviation between the contact time,which does not affect the comparison of droplet impact morphology.CFD numerical simulation can be used as a pre-processing step of bionic samples.After verifying the hydrophobicity of the structure by computer,we can decide whether to process the bionic samples of such microstructures.It provides a convenient,fast and effective means for the study of superhydrophobicity.In order to further apply superhydrophobic biomimetic samples to engineering,this paper continues to test the infiltration of bionic samples at different tilt angles.The droplets collide with the bionic specimens with inclination angles of 30°,45°,and 60°,respectively.Compared with the surface of the smooth sample with the same angle,after the droplets hit the surface of the bionic sample,they will bounce off the surface of the sample after spreading and shrinking.After the droplet hits the surface of the smooth sample,it can only flow slowly along the downward gravitational component due to the large viscous force.The friction force between droplet and solid surface decreases with the increase of contact angle.The superhydrophobic surface can effectively reduce the fluid mechanical resistance and improve the working efficiency of fluid machinery.