Study On Drag Reduction Characteristics Of Bionic Non-smooth Surface Of High-speed Train And Its Impact On Noise

With the improvement of various supporting facilities in the field of rail vehicles,the expansion of train mileage and the continuous increase in operating speed,research on trains is focusing on how to reduce its energy consumption and improve its ride comfort.This study is based on the boundary layer theory.The research object is a large number of CRH3 vehicles on existing lines.Non-smooth surfaces are applied to different parts of the train to explore its influence on the aerodynamic resistance and aerodynamic noise of the train.Based on the current situation of domestic and foreign high-speed trains,the necessity of research on drag reduction and noise reduction of high-speed trains is explained.From the perspective of drag reduction and noise reduction,a brief description of the development history of the appearance of domestic trains is made.Noise technology has been systematically summarized;the application of non-smooth surfaces to other objects to achieve drag reduction and noise reduction has been combed;domestic and foreign scholars in the past two decades have summarized non-smooth surfaces in different parts of high-speed trains.ResearchRelevant theoretical foundations are the basis for various experiments.In order to set the experimental conditions more accurately,a basic description of theory of aerodynamic resistance and noise of high speed trains was done.Based on the air continuum assumption,the mass conservation equation,momentum conservation equation,energy conservation equation,turbulence control equation,and Lighthill acoustic analog equation are introduced.And then the boundary layer theory was explained with formulas and graphs.A simplified model of CRH3 was established through the 3D modeling software PRO-E;the 3D model was then imported into ICEM CFD for mesh division;the divided mesh was imported into FLUENT software for simulation calculations,and two non-smooth surfaces witch include convex hull and concave pit were analyzed.The variation of aerodynamic resistance and aerodynamic noise of convex hulls and dimples with different parameters at different positions of the train were analyzed,and were compared with a smooth surface train to check its drag and noise reduction performance.The analysis results show that the array distance between the individual elements in the non-smooth structure has the most obvious drag reduction effect on the non-smooth surface.When the convex hull distance is 460 mm,height is 10 mm,and radius is 40 mm,and,and the structure is in the streamlined area of the train head and tail,the drag reduction is 1.77%.When the convex hull array distance of the streamlined area is 410 mm,the height is 10 mm,and the radius is 40 mmm,the noise reduction effect is obvious everywhere on the train surface.When the dimple array distance is 350 mm,the depth is 10 mm,the radius is 80 mm,and it is located in the streamline area of the train head and tail,the drag reduction effect is the most obvious,reaching 5.26%.When the streamline area pit array distance is 350 mm,the depth is 10 mm,and the radius is 60 mm,the noise reduction effect is significant everywhere.Finally,by studying the aerodynamic characteristics of the train body,the drag reduction and noise reduction mechanisms of non-smooth surfaces after application are explained from two perspectives,macro and micro.The results show that the application of non-smooth surfaces can effectively reduce the viscosity of train bodies.The resistance of the train increases the differential pressure resistance of the train,but the non-smooth surface of the appropriate parameter decreases the viscosity resistance of the train more than the increase of the differential pressure resistance,which reduces the overall aerodynamic resistance.In addition,the non-smooth surface at the appropriate position can reduce the amplitude of the pressure pulsations between the surface layers reduces the noise value.