Numerical Study Of Aerodynamic Drag Formation Mechanism Of High-speed Train

With the continuous improvement of the high-speed train,aerodynamic drag has become the main source of resistance.Aerodynamic drag is an important index for energy saving and consumption of trains.The aerodynamic drag becomes more intense and complicated when the train meeting and running in the tunnel as the intersection is subjected to alternating pressure waves.For the demand of energy saving of the train,as well as the consideration of the train operation,environmental and economic factors and the formation mechanism distribution characteristics of the aerodynamic drag influencing factors are necessary to study deeply.In this dissertation,three-dimensional numerical simulation is adopted.The aerodynamic drag characteristics,formation mechanism,distribution characteristics of the certain type of Chinese standard emu in different operating conditions and the influence of the pressure wave and the velocity parameters are studied in this paper.Finally,the tunnel factors running in the tunnel are obtained.All the work,provide important technical support for train optimization design and related standard correction.Its main work is as follows:(1)Based on a single car stable operations in the open air,the distribution of pressure field,velocity field and vortex structure around the train were revealed through three-dimensional numerical simulation.The formation mechanism and distribution characteristics of total drag,differential drag and frictional drag are studied by combining the flow field characteristics of the train.The research shows that the pressure difference between the head and tail car and the friction between the air and the wall surface of the train are the main reasons for the pressure difference and friction drag of the train during the operation.The head and tail of the car and bogie system account for the main drag proportion.(2)As two trains meeting in the open air,base on the flow characteristics and pressure fluctuation of the train at different times,the aerodynamic drag formation mechanism and distribution characteristics in the process of train meeting were studied.The study shows: aerodynamic drag of the whole car increase first and then decrease;decrease first and then increase;increase first and then decrease at the next three times: meeting by two heads,head and tail,two tails.This change is directly related to the pressure change of the head and tail car and the influence of the object train pressure field.Differential pressure drag plays a leading role in the meeting of the train.The speed of the train has little influence on the drag of the parts and the carriages,and the proportion is mainly concentrated in the head and tail car and the bogie system.(3)In the case of single train passing through the tunnel,the characteristics of the flow field at different time of the tunnel and the pressure fluctuation curve of the head and tail vehicle are given,and the mechanism and distribution characteristics of the drag change are analyzed.The research shows that the charge of the train drag is related to the direction of the compression wave and the expansion wave.When the high-speed train passes through the tunnel,the most adverse moment of the train's aerodynamic drag is that the initial expansion wave of the car is completely acting on the train,at the same time the aerodynamic drag of the train reaches its peak.The change of head-tail vehicle drag plays a leading role in the change of total drag.At different speeds,The ratio of average aerodynamic drag factor in tunnel situation to that in open air situation which named train average tunnel factor is about 1.2.(4)In the case of two trains meeting in the middle of the tunnel,by comparing the flow field characteristics in the process of train meeting and pressure wave characteristics,formation mechanism of the drag in the process of train meeting distribution characteristics are studied,and the maximum of the drag in the train through the tunnel of the entire process and the trains meeting process are analyzed and compared.The study shows that when the train is meeting in the tunnel,the train has a strong negative pressure characteristic due to the rapid displacement of the lateral flow of the train.The effect of the meeting process on the train drag is far greater than that of the pressure wave.In the process of the meeting of two cars in the tunnel,the amplitude of the pressure difference and the friction drag amplitude of the train are alternated,and the pressure drag is dominant in the remaining moments.The aerodynamic drag of the train fluctuates greatly due to the fluctuation of the tunnel pressure,but the fluctuation is mainly caused by the head and tail of the car.At different speeds,the train average tunnel factor is about 1.5.