Large Eddy Simulation Study Of Outside The High-Speed Train Unsteady Flow Characteristics Under Crosswind

When the train runs at high speed on the open line,the aerodynamic problems caused are more and more obvious.The external flow field of the train has strong unsteady characteristics,which will have a certain impact on the stability of the train’s operation,energy consumption and the surrounding environment along the railway.Especially when encountering a crosswind,the flow field structure around the train will change greatly compared with when there is no crosswind.The flow field on the leeward side and the windward side is extremely asymmetrical,and the fluctuations are more severe.The pressure distribution and aerodynamic load on the surface of the train Great changes have also taken place,especially the unsteady characteristics of the flow field at the tail,head and leeward side of the train are more prominent,making the aerodynamic load on the train have strong unsteady characteristics,which will seriously affect the stability of the train.The impact may even cause the train to overturn in severe cases.Therefore,it is necessary to study the unsteady characteristics of the external flow field of highspeed trains under crosswinds,which can provide reference for the safe operation of crosswinds.In this paper,a 1:1 model of a certain type of high-speed train is selected as the research object,the speed is 250km/h,the STAR-CCM+ software is used,and the large eddy simulation method is based on the three-dimensional,unsteady,incompressible turbulent flow model,and the finite volume method is used.,Numerical simulation analysis of the unsteady characteristics of the flow field outside the train.First,under the condition of no crosswind,numerical simulation is performed when the train is running at high speed on the open line to study and analyze the unsteady characteristics of the external flow field of the train,analyze the pressure distribution around the train,the velocity field,the structure of the tail flow field,and the various trains.The distribution and formation mechanism of the aerodynamic force experienced by the carriage and the entire vehicle.Secondly,under the crosswind conditions with wind speed of 30km/s and three wind angles of 30°,60° and 90°,the unsteady characteristics of the flow field outside the train when the train is running on the open track are simulated and studied,and the train is analyzed.The surrounding pressure distribution,velocity field,leeward side and the structure of the flow field at the rear of the train are compared and analyzed.The influence of the wind direction angle on the flow field is compared and analyzed with the flow field characteristics under no wind conditions.Finally,study the influence and mechanism of wind direction angle on the distribution and change of aerodynamic load on the train,especially the influence mechanism on lateral force and overturning moment,and compare and analyze the dangerous wind direction angle and the most dangerous part of the car under crosswind.According to the analysis of simulation calculation results,the following conclusions are obtained:(1)Compared with the condition of no wind,the unsteady characteristics of the external flow field of the train are more obvious.Under the crosswind,the pressure distribution on the windward and leeward sides of the following train is extremely asymmetric,so that a large pressure is generated on both sides of the train.Poor,increase the risk of overturning the train;different wind direction angles will also cause different degrees of deviation of the maximum positive pressure area of the train.The greater the wind direction angle,the greater the pressure difference between the windward side and the leeward side.When the wind direction angle is90°,the lateral force and overturning moment of the train are the largest,and the overturning risk is also the greatest.(2)Under crosswind conditions,the lateral force and overturning moment experienced by the leading car of the train are the largest,accounting for more than 58% of the entire vehicle,which is far greater than the lateral force and overturning moment experienced by the intermediate car and the trailing car.Therefore,the leading vehicle is the most dangerous position for the train to roll over under crosswind conditions,and rollover is often the first to start from the leading vehicle.