Numerical Simulation Reseach On Aerodynamic Drag Characteristics Of High-speed Train Running In The Open Air

Aerodynamic drag is one of the key aerodynamic indicators that affect the speed of high-speed trains.Good aerodynamic drag characteristics is also an important signs of energy saving and environmental protection.Experimental studies showed that the aerodynamic drag of high-speed trains was linear with the square of the speed of train,when the speed goes up to 200km/h,the aerodynamic drag constitutes more than 70% of the total drag.when the speed goes up to 300km/h,the aerodynamic drag constitutes more than 85% of the total drag.The higher the train speed,the higher percentage of air drag to total drag.Therefore,the key to reducing traction power,reducing energy consumption and improving economic efficiency is the aerodynamic drag reduction of high speed trains.This paper mainly used the STAR-CCM+,a kind of computational fluid dynamics software developed by CD-adapco company to simulate aerodynamic drag of high-speed train steady-state running in the open air and when two trains pass by each ather in the open air.Flow equation in this paper is RANS,three-dimensional,turbulence N-S equation and choose SST k-? model to simulate the flow field around the high speed train.The finite volume method is used for Computational domain discretization and SIMPLE that is a kind of numerical method is used to solve the discrete equations.In this paper,the full y+ that is a kind of wall treatment method is used to solve the air flow in the wall boundary layer.In this paper,the aerodynamic drag characteristics of vehicle and bogie,pantograph and windshield are studied when the high-speed trains steady run in the open air or two trains pass by each ather,It also analyzes the influence of train speed and train formation length on aerodynamic drag when running in the open air.The main conclusions of this paper are as follows:(1)When the train steady run in the open air,the head car and the tail car has a greater impact on the total aerodynamic drag of the train,accounting for 33.7% of the total aerodynamic drag of the train.The pressure drag of the head car and the tail car is greater than their shear drag,the pressure drag and shear drag of middle cars are almost equal.(2)When the train steady run in the open air,the bogie systems has a great influence on aerodynamic drag,which accounts for 30.8% of the total aerodynamic drag,the aerodynamic drag of the bogies and the bogie cavities are almost as the pressure drag;The aerodynamic drag of windshields accounts for 30.8% of the total aerodynamic drag,their pressure drag are much greater than the corresponding shear drag;Pantograph systems accounted for 8.5% of the total aerodynamic drag of the train,also mainly for the pressure drag.(3)When the train steady run in the open air,the aerodynamic drag of the train is proportional to the square of the speed of the train;The aerodynamic drag of the train is linearly related to the length of the train,the aerodynamic drag of the head car and tail car is not related to the length of the train.(4)When two trains pass by each ather in the open air,the pressure drag of the head car and tail car is greater than the shear drag,there is little difference in the pressure drag and shear drag between the middle cars;The variation trend of the pressure drag of the every car is the same as that of the corresponding total aerodynamic drag,so the pressure drag is the main reason of the unsteady flow around the train.(5)When two trains pass by each ather in the open air,the aerodynamic drag of bogies,windshields and pantographs are almost as pressure drag,the variation trend of the pressure drag is the same as that of the corresponding total aerodynamic drag,and The change of shear drag is small,showing a steady characteristic.(6)When two trains pass by each ather in the open air,the peak value of aerodynamic drag of train,head car and tail car is proportional to the square of speed.There is a linear relationship between the peak value of aerodynamic drag of the train and length of train,the length of train has little influence on the peak value of aerodynamic drag of the head car and tail car.