Investigation On The Aerodynamic Forces Characteristics Of Railway Vehicles In Turbulent Crosswinds

This thesis reviews the development history of the China High-Speed Railway,the study status of the wind-vehicle-bridge system and the problems related to the aerodynamic characteristics of railway vehicles under turbulent crosswinds.An investigation of aerodynamic admittance is also conducted.It is found that the spatial distribution characteristics of aerodynamic forces exert a significant influence on railway vehicles.A method is developed combining wind tunnel tests with theoretical analysis.Based on sectional model pressure-measuring wind tunnel tests,the pressure distribution characteristics,mean aerostatic characteristics and spatial distribution of buffeting forces on railway vehicles are investigated.The coherence functions of the buffeting forces and three-dimensional aerodynamic admittance are obtained.The aerodynamic characteristics of moving railway vehicles are then studied in the wind tunnel tests using the force measuring method.Firstly,an introduction is made to the two-dimensional aerodynamic admittance function of the aerofoil,the influence of the finite length of the models and the three-dimensional characteristics on the aerodynamic admittance of the aerofoil and the aerodynamic admittance of the bluff body and buffeting force model.Meanwhile,the aerodynamic admittance functions and identified methods for the bluff body section are summarized.Turbulent wind fields with different turbulent scales are simulated in the wind tunnel.The characteristics of turbulence,including the turbulence intensity,the turbulence length scale,the wind spectrum and the span-wise correlation characteristics are analyzed.Based on the theory of isotropic turbulence,the longitudinal wind spectrums of the moving points are derived and analyzed.The influence of wind speed,train speed and wind yaw angle on the peak values of the wind spectrums and the corresponding frequencies are investigated.Secondly,the mean and fluctuating pressure distributions,aerostatic characteristics and spatial distributions of the buffeting forces on still railway vehicles on truss girders are analyzed in two different turbulent flow fields.Influence factors,including the wind angle of attack,turbulence,railway vehicle positions and span-wise distances are investigated.The coherence functions of the buffeting forces are obtained.The results show that the larger the turbulence length scale,the better the span-wise correlation characteristics of the buffeting forces.The influence of the wind angle of attack on the span-wise correlation characteristics of the buffeting forces is minimal.When the railway vehicle is on the leeward side of the girder,the span-wise correlation of the lateral buffeting force is worse.However,an opposite variation trend can be seen for the lift buffeting force and buffeting moment.The span-wise correlation characteristics of the buffeting force decrease as the span-wise distance increases.Thirdly,the three-dimensional aerodynamic admittance of trains in two different turbulent flow fields are obtained based on the concept of equivalent aerodynamic admittance.The results show the relatively large influence of turbulence on the aerodynamic admittance.The larger the turbulence length scale,the larger the values of the aerodynamic admittance.The aerodynamic admittance stays roughly the same between wind angles of attack of-3° to 3°.The influence of the wind angle of attack on the aerodynamic admittance mainly occurs at the low-frequency region.Meanwhile,the aerodynamic admittances are greatly influenced by the positions of the trains.Finally,the mean aerostatic characteristics,buffeting force spectrums and aerodynamic admittances of the moving railway vehicles are investigated based on the high-speed moving railway vehicle wind tunnel tests.The aerodynamic admittance functions are also concluded.The results show that the distribution of the buffeting force spectrum energy of the moving trains is relatively uniform for different frequencies which are mainly located at the low-frequency region of the static train.The aerodynamic admittance value of the static train decreases as the dimensionless frequency increases,while for the moving train,the aerodynamic admittance value increases.The higher the train speed,the larger the aerodynamic admittance values.The research results on the aerodynamic characteristics of railway vehicle(including the aerostatic characteristics and spatial distribution characteristics of buffeting forces)in turbulent turbulent crosswinds provide calculation parameters for the wind-vehicle-bridge coupling analysis and the comfort evaluation of the high-speed railway bridges.The aerodynamic characteristics results of railway vehicles may offer a reference.