Prediction And Control Of Aerodynamic Noise Of High Speed Pantograph In Low Temperature Environment

Low temperature is a common working condition for high-speed trains.Decrease in ambient temperature makes the physical properties of air change,thus affecting the aerodynamic and aeroacoustic performance of the pantograph.In this thesis,the prediction and control of aerodynamic noise from a high-speed pantograph moving in low temperature environment are studied by theoretical analysis and numerical simulation.Firstly,the flow field around the pantograph is simulated for speeds at 200 km/h,300km/h and 400 km/h and temperatures at-50 ℃,-20 ℃ and 15 ℃ based on three-dimensional compressible viscous fluid model,and the far field aerodynamic noise of the pantograph is calculated by the FW-H equation.Then,the variation laws of pantograph aerodynamic drag,aerodynamic lift and aerodynamic noise at different temperatures and the effect of air compressibility are analyzed.The results show that the pressure drag and viscous drag of the pantograph increase with temperature decrease,and the total aerodynamic drag increases by14% and 30%,respectively,when the ambient temperature decreases from 15 ℃ to-20 ℃ and-50 ℃.And the higher the velocity is,the more significant the influence of temperature on aerodynamic drag is.In low temperature environment,the fluctuation of aerodynamic lift of the panhead is more intense,and this may have a negative effect on the quality of current collection.Low temperature increases the fluctuating pressure amplitude on the pantograph surface and makes pressure fluctuation more intense,giving rise to the far-field aerodynamic noise increase.At the speed of 400 km/h,the average of the sound pressure level at measuring points on a horizontal semi-circle with a distance of 7.5 m from the pantograph is predicted to increase by about 1.4 dB if the temperature drops from 15 ℃ to-20 ℃,and by about 3.2 dB if the temperature drops further to-50℃.However,the spectrum characteristics of aerodynamic noise at different temperatures are very similar.The difference of the increase of sound pressure level caused by the decrease of temperature at different velocities is small.The change of air density caused by change in ambient temperature is the main factor affecting pantograph aerodynamic force and aerodynamic noise at different temperatures.Under the calculation conditions of this thesis,relative accurate results of aerodynamic drag and noise sound pressure level of the pantograph can also be obtained by using incompressible model.Because of that the low temperature can deteriorate the aerodynamic performance of the pantograph,it’s necessary to consider the influence of noise reduction measures on the aerodynamic force of the pantograph when controlling the pantograph noise in low temperature environment.Then,the position of the main aerodynamic sound source on the surface of the pantograph is located by the CFD results,and the generation mechanism of pantograph aerodynamic noise is understood by analysing the flow field around the pantograph.On this basis,the contribution of each component of the pantograph to the total noise and the spectrum characteristics of the pantograph aerodynamic noise are analyzed.The results show that the distribution of aerodynamic sound sources on the surface of the pantograph is similar under different temperatures because of the similar vortex structure of the pantograph at different temperatures.The areas where the vortex shedding or impacted by the trailing vortex of the upstream components are the main sound sources.The far-field aerodynamic noise of the pantograph is mainly contributed by the bottom and top areas of the pantograph,and the farfield noise energy is concentrated in the frequency band below 800 Hz,and the peak values in the spectrum are mainly generated by the base frame,balance arm and the rear sliding plate.Finally,the influence of pantograph cavity on aerodynamic force and aerodynamic noise of pantograph area is studied.Based on this,an eight-car train model with pantograph sinking installation is established,and the raising mode which is beneficial to drag reduction and noise reduction is determined by using steady RANS method andBroadband Noise Source model.The results show that,compared with the way of external installation,the sink installation(using pantograph cavity)facilitates to reduce the aerodynamic drag of the pantograph area and has little effect on the lift of the top area of the pantograph.No matter which installation mode,the aerodynamic noise from the pantograph area is dominated by the pantograph itself;whether the pantograph is raised or folded,the existence of the pantograph cavity can significantly reduce the noise in the frequency band below 315 Hz from the pantograph,while for the frequency band above 315 Hz,the pantograph cavity could control the aerodynamic noise from the folded pangograph more effectively.There is little difference in the total drag of the pantograph area between raising the front pantograph and raising the rear pantograph,but the total sound power level of the pantograph area when raising rear pantograph is about1 dB lower than front pantograph.