Research On Prediction Of Aerodynamic Noise Of High-speed Trains Based On Component Recombination

The higher running speed of high-speed trains,the greater the aerodynamic noise will be generated.The excessive aerodynamic noise not only causes environmental pollution but also brings negative subjective feelings to passengers and people along the railway.At present,aerodynamic noise has become a key issue restricting the further speed-up of high-speed trains.To break through this obstacle,it is necessary to thoroughly study the radiation characteristics of high-speed train noise sources and quantify the magnitude of the high-speed train’s far-field radiated noise.Based on CFD and aeroacoustics theory,a numerical calculation model for aerodynamic noise of high-speed trains is established.It is very important to study the aerodynamic behavior characteristics,noise source distribution characteristics,noise source far-field radiation characteristics,and frequency spectrum characteristics of high-speed train components and the train.In general,high-speed trains exist in the form of 8 or 16 formations.It is also of great significance to predict the aerodynamic noise of long marshalling high-speed trains.Based on the similarity theory of fluid flow and aeroacoustics,the relationship between the far-field sound pressure level of the dipole noise source and the speed,characteristic size,and position of the noise evaluation point is derived.The aerodynamic noise calculation model of the finite-span cylindrical rod is established,and the aerodynamic noise is numerically simulated using the steady SST k-? turbulence model,unsteady DES and FW-H acoustic model.The results show that when the Reynolds number of the fluid flow is within the range of the automatic model region,Sr and Ma are important criterion numbers to ensure the aeroacoustic similarity between high-speed train models.The radiation characteristic of a cylindrical rod as a noise source belongs to the typical dipole noise source radiation,and it has obvious acoustic directivity.The sound pressure level at the noise measurement point perpendicular to the incoming flow direction is the largest,and the sound pressure level at the noise measurement point parallel to the incoming flow direction is the smallest.The sound pressure level at the measurement point is linearly related to the logarithm of the sixth power of speed,inversely proportional to the square of the distance,and proportional to the square of the characteristic scale of the object.Under the premise that the change in Reynolds number has little effect on the flow state of the components of the pantograph and the frequency of vortex shedding satisfies that the Sr number is approximately equal,four pantograph models with different scaled size,semipantograph models and full pantograph models are established to carry out the numerical calculation of aerodynamic noise.The model scaling law of the high-speed pantograph and the far-field sound pressure level radiation characteristics,spectrum characteristics,and dominant frequency generation mechanism of the pantograph are studied.At the same time,for the pantographs with geometric shapes that are approximately symmetrical,the sound field similarity between the semi-pantograph models and the full pantograph models is studied.The results show that the model scaling barely does not change the flow field characteristics around the pantograph.The pseudo-sequence structure of the pantograph tail vortex almost does not change with the model scale,and the main vortex shedding frequencies have nearly multiple relationships with the scaled model.Flow fields around pantograph models with different scaled size have similarities.The smaller the scaled size of the model,the greater the impact of the sound pressure level of the pantograph far-field noise measurement point.When the scale ratio of the model is 1: 8,the sound pressure level changes of the pantograph far-field longitudinal noise measurement point are less than 2.0 d BA.The scaled size almost does not change the sound pressure level characteristics of the far-field lateral and vertical noise measurement points,and has a certain effect on the sound pressure level characteristics of the longitudinal noise measurement points.The semi-model and full-model pantograph have a certain similarity in the flow field around the pantograph.The total sound pressure level of the full model pantograph at the noise measuring point can be obtained by the superposition of the sound pressure level of the noise measuring point using the semi-model pantographSeveral high-speed train models with different degrees of simplification are established for the calculation of aerodynamic noise.The SST k-? turbulence model and DES are used to calculate the external steady and unsteady flow fields around the high-speed train,respectively.Based on the numerical calculation results of the unsteady flow field,the FW-H equation is used to calculate the aerodynamic noise of the high-speed train in the far-field.The relationship between the aerodynamic noise sources of all components and entire train aerodynamic noise sources is studied.The stepwise approach is prosposed to predict the farfield noise of the entire high-speed train.The results show that the radiation noise of the whole train can be approximated by the superposition of the radiation noise of all components.The sound source information of each component is obtained through high-speed train models with different degrees of simplification,and the radiation noise magnitude of each component is further obtained.It is feasible to obtain the radiation noise of the whole train based on the principle of energy superposition.The difference between the combined sound pressure level obtained by the stepwise approach and the average sound pressure level obtained by the calculation method of the whole vehicle model is 1.92 d BA.For the aerodynamic noise prediction of long marshalling high-speed trains,numerical calculation models for aerodynamic noise of high-speed trains with different marshalling numbers are established.Unsteady flow fields are calculated using the DES.Based on the FWH equation,the noise along the trains with different marshalling numbers is predicted.The results show that the distribution law of aerodynamic noise in the far-field barely does not change with the variaton of marshaling number.The larger the marshalling numbers of train,the greater the aerodynamic noise in the far-field of high-speed trains.When every train body is used as a source of aerodynamic noise,the distribution of far-field aerodynamic noise along the track side is similar.The noise for the long marshalling train model can be predicted with the calculation results of the short marshalling train model.The half train models with different marshalling numbers are established for the numerical simulation of aerodynamic noise.The results show that the noise distribution characteristics of the half-model trains are consistent with the noise distribution of the full-model trains.The noise for the whole train model can be predicted with the calculation results of the half trains.The two methods for calculating the aerodynamic noise of the long marshalling train model can provide a reference for the future development of the aerodynamic noise of the long marshalling train.