The Study On Aerodynamic Characteristics And Operation Safety Of Fast Freight Car Under Crosswinds

With the increase of train speed,the influence of cross wind on the safety of train operation becomes more and more significant.The shape of freight cars is mostly blunt body structure,and the surface flow field of the train is more complicated.The height of the center of mass is different under different loading conditions,under the influence of crosswind,the operating status will change dramatically.In severe cases,the safety of train operation will be threatened.Based on the theory of fluid mechanics and multi-body system dynamics,this paper analysis the safety of fast freight cars under crosswinds,and provides a theoretical basis for the safe operation of fast freight cars.Based on the three-dimensional,steady,incompressible flow and standard k-ε twoequation turbulence model,this paper uses fluid simulation software FLUENT to establish a fast freight truck aerodynamic model,calculates the flow field around the fast truck under different wind speeds,wind angles and vehicle speeds,The flow field characteristics and aerodynamic load characteristics are analyzed and studied the influence of different vehicle speeds,wind speeds and wind direction angles on aerodynamic loads.Due to the difference in geometric shape,there is a big difference in the distribution trend of the aerodynamic forces and aerodynamic moment between the locomotives and trucks under the same conditions,and analyzed the reasons for the difference.Based on multi-body dynamics theory,this paper uses SIMPACK software to establish a fast truck system dynamics model,and analyzed the dynamic performance of empty and heavy vehicles under the influence of no cross wind,and adopts the GB/T 5599-2019 as the dynamics performance evaluation standard,the result shows that the critical speed of snake motion instability meets the design requirements under the condition of empty and heavy trucks with new wheels and limited wheels.the quality and stationarity indicators of the 80km/h～176km/h speed range meet the standard limits,Under the four curve conditions,the derailment coefficient,wheel load reduction rate,and wheel axle lateral force can all meet the operating requirements,and the heavy vehicle has better operating performance under the same operating conditions.In order to study the running performance of fast freight cars in crosswind environment,the aerodynamic load was loaded into the system dynamics model,and analyzed the effects of wind speed,wind direction and vehicle speed on the straight-line running performance of empty and heavy vehicles,and the variables were determined through regression analysis.Calculate the maximum safe operating speed of empty and heavy vehicles under straight-line conditions.In order to study the safety performance of fast freight cars when passing through curves of different radiuses under the action of crosswinds,the train derailment coefficient,wheel load reduction rate and axle lateral force indexes of fast freight cars under cross wind are calculated.The result shows that under the influence of wind load,the three indicators have increased to varying degrees.Among them,cross wind has the greatest impact on the wheel load reduction rate when the train is running in a curve.The operation performance of heavy vehicles is better than that of empty vehicles.And the maximum allowable wind speed for safe operation of fast freight cars under different working conditions is obtained.The fast freight car has high speed,light weight and blunt body shape.The result shows that the cross wind has great influence on the dynamic performance of the fast freight cars,especially in the curvilinear running state.When studying the dynamic performance of the fast freight cars,the influence of the cross wind on its dynamic performance cannot be ignored.