Research On Aerodynamic Characteristics And Change Rules Of Vehicle Piston Wind In Vacuum Pipeline

Based on the method of computational fluid dynamics,this thesis uses the two-dimensional and three-dimensional compressible model and dynamic grid technology to numerically calculate the aerodynamic characteristics and changing law of the piston wind in the vacuum pipeline traffic system,analyzes the movement law of the piston wind in vacuum pipelines,and studies the effect of different blocking ratios,vacuum degrees,driving speeds and other conditions on the piston wind,providing a reference for the further engineering application of the vacuum pipeline transportation system.Firstly,the thesis systematically introduces the basic characteristics of the piston wind,describes the boosting efficiency of the piston wind and the flow of annular flow field,and selects an appropriate basic control equation and turbulence model according to the characteristics of the vacuum pipeline transportation system.And the dynamic grid setting and meshing in the simulating numerical calculation of the computational model of the vacuum pipeline transportation system are introduced and analyzed in detail.Subsequently,the thesis carries out a numerical simulation of the two-dimensional model of the vacuum pipeline transportation system and analyzes the movement law of the piston wind in the vacuum pipeline.The analysis shows that when the train is running in the pipeline the air in front of the train will be squeezed by the train,leading to the increase of the air density and pressure;that some air will be squeezed from the front of the train through the annular to the rear of the train;and that the air behind the train will expand,leading to the decrease of the air density and pressure.Compression waves are generated by the compression of the air and expansion waves the expansion of the air.They will spread along the pipeline and also contribute to the aerodynamic drag of the train.Then the thesis analyzes the variation rule of the piston wind in a two-dimensional model of a vacuum pipeline transportation system.The analysis shows that an increase in the train blocking ratio will result in an increase in the flow deviation between the front and rear of the train,which in turn will increase the aerodynamic resistance of the train.At the same time,the greater the blockage ratio of the train is,the greater the energy of the Mach wave will be.Also,as the trainpressure increases the flow deviation between the front and rear of the train will increase,increasing the aerodynamic resistance of the train.Meanwhile,the greater the pressure of the train is,the greater the energy of the Mach wave will be.Whereas the train speeds,the flow deviation between the front and rear of the train will also increase,leading to the rise of the aerodynamic resistance,but with the growth of the train speed,the upward trend of the aerodynamic resistance of the train will slow down.Finally,through the numerical simulation of the three-dimensional model of the vacuum pipeline traffic system,the thesis analyzes and validates the simulation results of the two-dimensional model.The analysis shows that when the train is running in the pipeline it will indeed produce the expansion wave and the compression wave,both of which will affect the aerodynamic resistance of the train,but the Mach-wave energy in the three-dimensional model is obviously smaller than that in the two-dimensional model,resulting in a slighter influence on the aerodynamic resistance of the train.The changes in the blocking ratio,pressure,and speed will also cause the change of the piston wind movement,which will affect the aerodynamic resistance of the train.However,compared with the 2D model the resistance value of the 3D model will decrease on the whole,and the rise of the aerodynamic resistance of the train will only slow down at a higher speed of 440 m/s.