Study On The Drag Reduction Mechanism Base On Soft Elastic Fluff Of Dragonfly Body Surface

With the shortage of non-renewable resources,efficient utilization of resources has become the goal of human beings.In the field of transportation,energy conservation and drag reduction have become the key to reduce energy consumption.Based on the study of the physiological structure and surface characteristics of the flexible elastic fluff on the dragonfly body surface,this paper designs the flexible elastic fluff surface,explores the drag reduction characteristics of the fluff surface through the orthogonal test method,and takes the smooth surface as the reference surface,and uses the twoway fluid structure coupling simulation method to explore the drag reduction mechanism of the fluff surface.Firstly,the morphological parameters of the dragonfly body surface are measured and analyzed.The thoracic backplane with the most regular distribution of fluff is selected as the main research area,and the geometric size and Young's modulus of fluff in this area are measured.Based on the observation results and the design method of orthogonal test,16 groups of simplified models of flexible elastic fluff surface are established.The two-way fluid structure coupling numerical simulation of 16 groups of simplified models shows that the drag reduction effect on the surface of the flexible elastic fluff is the most significant by the length of the fluff,followed by the distance between the fluffs,the flow velocity and the diameter of the fluff.The optimal parameter combination of drag reduction effect on the surface of flexible elastic fluff is optimized: the length of the fluff is 200 ?m,the distance is 110 ?m,the flow velocity is 15 m/s,and the diameter is 2.5 ?m.The drag reduction effect is the best,and the maximum drag reduction rate is 12.428%.Taking the smooth surface as the reference surface to analyze the influence of the fluff surface on the flow characteristics in the near-wall region.The results show that due to the accumulation and blocking effect of flexible elastic fluff,the airflow gathers in this region,increasing the thickness of the fluid boundary layer;In addition,there is a low-speed vortex near the fluff,which suppresses the turbulent "rising",so the number and intensity of turbulence bursts are greatly reduced;The fluff can also weaken the impact of airflow on the boundary layer,reduce the shear stress and make the viscous resistance.Although the fluff structure will increase the differential pressure resistance,the increased differential pressure resistance is less than the decreased viscous resistance,so the overall resistance shows a downward trend.Finally,the smooth model and flexible elastic fluff model are processed by using reverse engineering technology and electrostatic flocking technology,and a complete test system is built to test the aerodynamic characteristics of the two models in a lowspeed DC wind tunnel.The test results show that the resistance value of the flexible elastic fluff model is smaller than that of the smooth model under different wind speeds,which verifies the correctness of the numerical simulation.