Research On Aeroacoustic Characteristics Of Hts Maglev Train In Low Vacuum Tube

In the field of rail transit,speed is the primary goal that people pursue.At present,traditional wheel-rail traffic is constrained by problems such as aerodynamic drag,wheel-rail adhesion,operation noise,serpentine instability,and bow-net relationship.It is difficult to achieve a significant breakthrough in terms of speed.In the frontier field of modern super high-speed ground transportation,the choice of maglev vehicles can avoid the frictional resistance between wheels and rails,but the inevitable objective environmental factors also come from the dense atmosphere on the ground,and the maximum economic speed of trains running on the ground generally does not exceed 400 km/h.The fundamental way to increase the speed can only be to change the density of the medium around the train to reduce the aerodynamic effect on the train.Therefore,the idea of combining low-vacuum tubes with high-speed maglev transport came into being,which would be able to achieve ultra-high-speed operation of 1000 km/h.The aerodynamic noise of the traditional high-speed train is proportional to the 6th to 8th power of the speed.The system is not completely vacuum,and the aerodynamic noise characteristics generated by the interaction between the flow field in the tube and the train become the focus of this study.This thesis uses ANSYS FLUENT software,based on the threedimensional,steady,compressible Reynolds average Naiver-Stokes equation and Realizable6)- double equation turbulence model to simulate the high-speed operation of hightemperature superconducting(HTS)maglev trains in low-vacuum tube.The aerodynamic characteristics,flow field status and noise source distribution of superconducting maglev trains are based on the steady-flow field.The detached eddy simulation model is used to calculate the unsteady flow field,and the FW-H equation is used to study the aerodynamic noise characteristics in the tube.The main contents are lised as follows:1.The current magnetic levitation system has been investigated.In view of the lowvacuum environment and ultra-high-speed operation scenarios,HTS system has been used as the carrier for low-vacuum tube traffic.With reference to the simulation of aerodynamic characteristics of high-speed trains,a three-car maglev train model was established and matched with different radius tube models.At the same time,a maglev train calculation model under the open environment was established to provide a calculation model for simulation analysis.2.Low-vacation tube can provide a low-pressure environment for maglev train operation,but it will make the flow field around the train more complicated.The study found that the aerodynamic drag experienced by the maglev train in the low-vacuum tube has an approximately quadratic relationship with the speed,an approximately proportional relationship with the air pressure in the tube,and a positive correlation with the blocking ratio.Taking the 350 km/h maglev train aerodynamic resistance of 18.45 k N as the economic index in the opening environment,the operating speed of 1000 km/h is achieved in the low-vacuum tube,and the air pressure in the tube needs to be controlled below 0.01 atm with each blocking ratio.3.Through the basic theory of fluid mechanics and aeroacoustics,it is found that the aerodynamic noise of the HTS maglev train in the low-vacuum tube is the same as that of the high-speed train,which is derived from the pulsating pressure generated by the interaction between the flow field and the train.The sound source and quadrupole sound source change rule is basically consistent with the aerodynamic resistance of the maglev train in the tube,but when the running speed of the HTS maglev train in the tube is greater than 600 km/h,the intensity of the quadrupole sound source is greater than that of the dipole sound source.4.Considering that the future low-vacuum tube may affect the environment along the line through the acoustic-vibration coupling,the thesis specifically considers the change rule of the dipole noise sources on the upper surface and the bottom surface of the low-vacuum tube wall.The analysis found that because the bottom surface of the tube is closer to the vehicle body,the intensity of the dipole sound source at the bottom surface of the vehicle body is greater than the upper surface of the pipeline.The effect of turbulence at the tail on the upper surface of the tube is greater than the bottom surface of the tube,engineering low-vacuum tube construction may consider adding tube wall damping materials to reduce environmental noise pollution along the line.5.In order to reduce the calculation time while ensuring accuracy,this thesis uses the method of detached eddy simulation to perform the transient calculation on the flow field based on the steady-state flow field.The calculated pressure fluctuation data of the flow field is Fourier changed and converted into the aerodynamic noise spectral characteristics.The analysis shows that under the condition of 1000 km/h,0.32 blocking ratio,0.05 atm vacuum degree.In the frequency range under 5000 Hz,the sound pressure level of the aerodynamic noise at the measuring point of the third vehicle decreases with the increase of frequency and tends to be stable.The higher sound pressure level is concentrated under the low frequency 50 Hz range,and the low-frequency characteristics are obvious.Other conditions remain unchanged.As the vacuum decreases,the sound pressure level at the measuring point gragually decreases.Lowering the air pressure value is helpful to reduce the aerodynamic noise sound pressure level,and its low-frequency characteristics are more obvious.It will operate in low-pressure tubes in the future.The design of the super-high-speed maglev train inside should fully consider the influence of low-frequency characteristics of aerodynamic noise on the vibration mode of the car body.