| With the increase of the speed of the train,the dynamic environment of the vehicle has been changed fundamental.The noise index has become an important factor limiting the speed of high-speed trains..With speed exceeding 300 km/h,aerodynamic noise contribute most to the noise pollution.Pantograph is one of the main aerodynamic noise sources of high-speed train.It is very important to study on the propagation characteristics of the aerodynamic noise of pantograph in order to improve the ride comfortability and reduce the noise pollution.Based on the Lighthill sound analogy theory,the size and distribution of surface dipole sound source of a pantograph on a high-speed train are calculated and analyzed.Based on this,the far-field aerodynamic noise of the pantograph is calculated.The main work,results and conclusions of this paper are as follow:1.Analysis of the external flow field of pantograph.The three-dimensional model of the pantograph and the finite element model of the flow field are established.The unsteady flow field of the pantograph is fully developed based on the large eddy simulation method.The external flow field of the pantograph has very strong unsteady characteristics,and high flow regions of the fluid is mainly concentrated in the support skateboards,hinge connection between upper frame and lower arm.A vortex shedding similar to a Carmen vortex can be observed in the pantograph flow field wake zone.2.Analysis of dipole source on the surface of pantograph.The surface fluctuating pressure in the flow field is converted to the surface dipole source with Fourier transform method.It is concluded that the strong aerodynamic sound source is mainly distributed in the support skateboards,shaft,the leeward end of the base,triangular region of the hinge mount and the lower arm;the surface aerodynamic noise source of pantograph is a broadband noise source;the trend of sound pressure spectrum curve of the dipole sound source at different speed is basically the same,and when the running speed of the train increases,the surface dipole sound pressure level increases and tends to shift towards high frequency.3.Analysis of aerodynamic noise in pantograph far field.Based on the surface dipole sound source,the distribution of the aerodynamic noise in the far field of the pantograph and the sound pressure level spectrum at the standard measuring point are calculated by the finite element method.Using the Strouhal number and the numerical calculation of flow around the cylinder,the peak frequency is estimated according to the minimum feature size of the pantograph,and its effectiveness is verified.The analysis results show that the peak frequency of the pantograph can be set as 3150Hz with the speed range of 300?500km/h.The acceleration of train speed will lead to the increase of aerodynamic noise of pantograph far field as well as the frequency value corresponding to the maximum sound pressure level.The high sound pressure level band of broadband noise continues to reach nearly 3000 Hz,and compared with the aerodynamic noise of the train body,the band of high sound pressure level of the continuous frequency is wider.4.Analysis of aerodynamic noise of pantograph far field considering train influence.After taking the influence of the train into consideration,the radiation characteristics of the dipole sound source at the low frequency of the pantograph are obviously changed,and the radiation characteristics in the high frequency band are basically unvaried.In addition,the far field noise of the pantograph undergoes a certain attenuation at each frequency.The attenuation at low frequency is larger,and its directivity changes obviously.As the frequency increases,the difference between the two is gradually reduced,and the amplitude of the attenuation also has a tendency to decrease.The sound pressure level of the far point of the pantograph is significantly reduced,and its further decrease occurs in the low frequency range,and the maximum sound pressure level of the pantograph is reduced by 4.39dB. |
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