Aerodynamics Analysis Of High-speed Train Exit Tunnel Under Cross Wind

China now has the capability to develop and operate high-speed(160km/h)express freight trains,which can meet the demands of modern society for rapid and safe transportation.Considering the sharp edges and higher speeds of the new express freight trains,their aerodynamic characteristics when passing through tunnels may differ from those of high-speed trains and ordinary freight trains.Therefore,it is particularly important to conduct in-depth research on their aerodynamic characteristics when running through tunnels.In response to this situation,this paper studies the aerodynamic characteristics of the new express freight trains during tunnel crossing in high wind environments.Based on the“virtual wind tunnel” technology,numerical simulation is used to solve the bottleneck problem of long experimental cycles,high experimental costs,and inability to reproduce real working conditions.This paper takes the new express freight train as the research object,and based on the three-dimensional,unsteady,incompressible Navier-Stokes equations and the standard k-εturbulence model,conducts numerical simulation research on the aerodynamics of the train during operation.The main research contents are as follows:(1)Create a train-tunnel coupling model for four grouped express freight trains running through tunnels;use a block region mesh partitioning method to divide the calculation model into well-meshed regions,and conduct numerical analysis of the flow field when the train runs at speeds of 140km/h and 160km/h in a 200-meter tunnel to study the formation mechanism of tunnel pressure waves;(2)Under the conditions of crosswind speeds of 15m/s,25m/s,and 35m/s at the tunnel exit,numerical calculations are performed on the flow field when the train passes through the tunnel,and the effects of different crosswind speeds at the tunnel exit on the pressure distribution on the train surface,the pressure distribution on the tunnel wall,and the variation of compression waves in the tunnel are compared and analyzed to analyze the aerodynamic force variation of the express freight train.(3)The variation trend of the pressure distribution on the train surface under crosswind conditions with wind speeds of 35m/s and wind direction angles of 30°,45°,60°,90°,120°,and 150° is compared and analyzed,and the variation rules of the aerodynamic drag,lift,and lateral force characteristics of the express freight train are studied.The research results show that the maximum pressure is generated at the nose of the lead car of the express freight train under different wind speeds.As the wind speed increases,the pressure on the windward side of the express freight train shows a sharp increase.Taking the nose of the lead car as an example,when the crosswind speed changes from 0m/s to 15m/s,25m/s,and 35m/s,the pressure measurement points on the windward side of the lead car are 802.5Pa,812.8Pa,917.8Pa,and1148.2Pa,respectively,and a negative pressure zone appears in the upper flow field area of the train under a crosswind of 35m/s.Under crosswind conditions,when the express freight train runs at 160km/h and the wind speed is 35m/s,taking the aerodynamic drag coefficient of the train as an example,when the wind direction angle is less than 90°,the headwind increases the aerodynamic drag coefficient of the train;when the wind direction angle is between 90° and 180°,the tailwind reduces the aerodynamic drag coefficient of the train.When the wind direction angle is 90°,the amplitude of the aerodynamic force on the train is the largest.