Study On Characteristics Analysis And Control Of Aeroacoustics Of High-Speed Trains

With the increasing of the train speed, aeroacoustics of the high-speed train has become an increasingly important part of the high-speed train noise. Study on the computation and control of aeroacoustics of the high-speed train has important significance. For the aeroacoustics issue of the high-speed train, the computational methods of exterior and interior aeroacoustics of the high-speed train were established. The characteristics of far-field radiation aeroacoustics of the main aeroacoustics source parts were analyzed. The multi-objective optimization design model of the streamlined head of the high-speed train was eatablished, and the streamlined head was optimized to reduce the drag force and noise. The aerodynamic computational model of the high-speed train in the vacuum tube in the low-pressure environment was established, the characteristics of aerodynamic drag force and aeroacoustics source of the high-speed train in the vacuum tube were studied.Based on the actual situation of the high-speed train running near the ground, starting by the FW-H equation and Kirchhoff equation respectively, the far-field acoustical integral formula of the high-speed train considering the ground effect was derived respectively using the semi-free-space Green’s function. The effect of ground acoustical impendance on the far-field aeroacoustics of the high-speed train was studied. The former free sound field is equivalent to superposition of sound field of realistic train and sound field of mirror train because of the ground effect. The normal velocities and force sources on the mirror train are the same as that of on the realistic train. Considering that the air medium tends to have movement, the far-field acoustics integral formula of the high-speed train considering the medium movement and the ground effect was derived from the generalized Lighthill equation.The aeroacoustic model method and mixed computational method for the computational of the far-field aeroacoustics of the high-speed train were established. The far-field aeroacoustics of the head and pantograph of the high-speed train was computed and analyzed. The sound pressure spectrum of the far-fied measure point computed by the aeroacoustic model method and mixed computational method is basically the same. The far-field aeroacoustics of the high-spped train head has broadband characteristics and the energy is mainly distributed between1800-2800Hz. The far-field aeroacoustics of the high-spped train pantograph has narrowband characteristics and the energy is mainly distributed between100-700Hz. The equivalent continuous A-weighted sound pressure level of the far-field measure point of the head and pantograph of the high-speed train has a linear relationship with the logarithm of the train speed. The shape of control lines of the train head has obvious effect on the far-field aeroacoustics of the high-speed train. The aerodynamic noise corresponding to the head with the combination of straight longitudinal profile line and the square horizontal section line is the smallest. The aerodynamic noise corresponding to the head with the combination of drum-shaped longitudinal profile line and the cone horizontal section line is the largest.The computational method of interior aeroacoustics of the high-speed train was established based on the computational fliud dynamics and statistical energy analysis. The computational model of interior aeroacoustics of the high-speed train was established based on the theory of statistical energy analysis. The fundamental parameters, i.e., modal density, internal loss factor and coupled loss factor, were determined. The average fluctuating pressure spectrums on the carbody subsystems were obtained using the large eddy simulation, and the interior aeroacoustics of the high-speed train was computed and analyzed. For the liner-weighted sound pressure level, the sound pressure level of the drive’s cab cavity and passenger compartment cavity has low frequency characteristics. For the A-weighted sound pressure level, the sound pressure level of the drive’s cab cavity and passenger compartment cavity has broadband characteristics. The sound energy of the drive’s cab cavity is mainly distributed between100-2000Hz, the sound energy of the passenger compartment cavity is mainly distributed between50-2000Hz.The linear-weighted and A-weighted sound pressure level of the drive’s cab cavity and passenger compartment cavity has a linear relationship with the logarithm of the train speed.The multi-objective optimization design method of the streamlined head of the high-speed train was established. The aerodynamic drag force and dipole noise source were set as optimization objectives, and the multi-objective automatic optimization design of the streamlined head of the high-speed train was carried out. The three-dimensional parametric model of the high-speed train was established using the CATIA software, and five optimization design variables were extracted. The automatically deformation of the streamlined head of the high-speed train was achieved using MATLAB program and CATScript script file. The automatic division of the aerodynamic computational grid of the high-speed train and automatic computation of flow field of the high-speed train were achieved using the script files and batch commands. The automatic update of optimization design variables were achieved using the multi-objective genetic algorithm NSGA-Ⅱ, then the automatic optimization design of the streamlined head of the high-speed train was achieved. From the research on the correlation between optimization objectives and optimization variables, the key optimization design variables which have effects on the optimization objectives could be obtained. Then the non-linear relationship of the key optimization design variables and optimization objectives was obtained. By contrasting with aerodynamic performances of the original streamlined head, the maximum reduction of the aerodynamic drag force of the optimized streamlined head is4.54%, and the maximum reduction of the dipole source of the optimized streamlined head is4.95dB. In order to reduce the computational time of the multi-objective optimization, the approximate computational model of aerodynamic of the high-speed train was established using the radial basic function neural network. In order to get a good approximate in the whole optimization design space, the inputs and outputs of the radial basic function neural network were obtained using the optimal Latin hypercube design. The error between the predicted values computed by the approximate computational model and actual values of the aerodynamic drag foece is less than1%. The error between the predicted values computed by the approximate computational model and actual values of the dipole noise source is less than3dB. The approximate computational model has a good approximate. The Pareto frontier computed by the approximate computational model is basically the same as that of computed by the actual model.The fluid model, mathematical model and numerical model of aerodynamic computation of the high-speed train in the vacuum tube in the low-pressure (0.01atm-0.1atm) environment were established. The effects of tube pressure, blockage ratio and train speed on the drag coefficient, aerodynamic drag force, dipole noise source and quadrupole noise source were studied. Setting the aerodynamic drag foece of a400km/h train in the open field under the standard pressure condition as a limit value, the best relationship between tube pressures, blockage ratios and train speeds for the vacuum tube high-speed transportation system was determined. In the low-pressure environment, the air flow in the evacuated tube can be described using a continuous model. The aerodynamic drag coefficient basically has nothing to do with the tube pressure or the train speed, which mainly depends on the blockage ratio. The aerodynamic drag force of the high-speed train is linear with the tube pressure, and square with the train speed, and also increases with the increase of blockage ratio. The dipole noise source and the quadrupole noise source of the high-speed train are almost linear with the logarithm of the train speed. When the train speed is600km/h, the quadrupole noise source is small and the dipole noise source has a dominate status. With the increase of train speed, the quadrupole noise source becomes apparent and has a dominate status. In order to simulate the air flow characteristics in the vacuum tube in the more rarefied environment, the lattice Boltzmann model for rarefied gas flow in the slip and transitional regime was established, and the second order velocity slip boundary conditions was studied. Guo model, Hisa model and Zhang model have a good perform. The rarefied gas flows in the slip and transitional regime were simulated using Guo model. When the rarefaction parameter is equal to1.64, the computed dimensionless velocity profile is good agreement with the dimensionless velocity profile given by Karniadakis, which verify the correctness of the computational model and computational program.