Numerical Simulation Of Aerodynamic Noise Of High-speed Train In The Exterior Flow Field

With the rapid development of high-speed railway,the running speed of the train is increasing and the noise problem is becoming more and more significant in recent years.As the main noise source of high-speed train,aerodynamic noise has a great influence on surrounding environment and ride comfort,which a thorough understanding should be obtained.In this thesis,the aerodynamic noise source and characteristics of high-speed train is studied by numerical simulation method based on the theory of fluid mechanics and aeroacoustics.Then,a comparative analysis of simulation results and noise test results is carried out.Specifically,this thesis studied the following aspects:1.Basic equations of aerodynamic acoustics are derived from the basic equations of fluid mechanics.Then combined with the actual operation condition,the theoretical model of aerodynamic noise of high-speed train is established.The generation mechanism of aerodynamic noise is analyzed theoretically and Lighthill acoustic analogy method is selected with the theory of computational aeroacoustics.2.Physical model of the three dimensional flow field of the high-speed train is established according to the theory of turbulence model.The external steady and transient flow field of the 250km/h,300km/h and 350km/h high-speed train is simulated by using the time average turbulence model and the large eddy simulation method respectively.Then,the turbulent intensity and fluctuating pressure distribution of train body,pantograph and bogie are obtained.Results show that the fluctuating pressure is significant in the train head and trailing vortex is formed by high speed airflow at the rear sides of the tail car.Disturbance of the pantograph on the external flow field is the largest and its vortex shedding is very strong.3.Based on simulation results of the external steady flow field,aerodynamic noise source on surface of the high-speed train is calculated by using the Broadband Noise Sources Model,then the noise characteristics are analysed.Results imply that the intensity of surface aerodynamic noise source weakens along with the order: pantograph,head car,bogie,tail car,air-conditioning dome.The distribution of each main noise sources is different.The surface sound power level of the high-speed train increased 3~4dB as the train speed increases by 50km/h between 250km/h ~300km/h.4.Based on Lighthill acoustic analogy theory,the far-field noise of high-speed train is calculated by using the FW-H equation.The aerodynamic noise characteristics are obtained by analyzing the sound pressure level and frequency spectrum characteristics of the monitoring points.The results show that sound pressure level is proportional to the train speed and its attenuation rate in the horizontal direction decreased gradually.At different speed condition,the frequency band corresponding to peak value of the sound pressure spectrum is different and its center frequency increases gradually with the increase of speed.5.The pass-by noise of Beijing-Shanghai high speed railway with the speed of 250km/ h and 300km/h is tesed.Then,its frequency spectrum is analyzed and compared with simulation results.The results show that simulation and test have the same variation trend of sound pressure level spectrum,but the sound pressure level of each frequency is different.When the train speed is 300km/h,the deviation of the sound pressure level is less than the one when the train speed is 250km/h.The spectrum characteristic of pass-by noise will be more similar to the one of aerodynamic noise when the train speed is over 300km/h.