Study On Aerodynamic Performance And Operation Safety Of High-speed Train In Considering Water Film Effect Of Train Body

In recent years,high-speed train technology of our country made rapid progress.With the increase of train speed,the aerodynamic load on high-speed train increases.China has a vast territory with a diverse range of climatic conditions,and high-speed railways are mainly located in the monsoon region,where thunderstorms and heavy rain are relatively common.When a high-speed train is running in a wind and rain environment,raindrops accumulate on the surface of the train to form a water film.The water film interacts with the flow field around the train,which further deteriorates the aerodynamic performance of the train and threatens the safety of the train operation.In view of this,this paper studies the water film distribution and flow characteristics of high-speed train body under rainfall environment and wind and rain environment.The influence of water film on the aerodynamic performance and operation safety of high-speed train are analyzed.Based on the SST k-ω turbulence model and the Euler-Lagrange discrete phase model,a reasonable aerodynamic model is established,and the rationality of the rainfall plane setting is verified.The Lagrangian wall film model is used to simulate the water film distribution and flow characteristics of the train body.The results show that raindrops accumulate on the train surface to form water film,and the thickness and coverage of water film expand with the increase of rainfall time.The shear stress on the top surface of the streamlined area head car is large,and the corresponding water film flow velocity is also large.Compared with rainless environment,when the rainfall intensity is 500mm/h,the average skin friction coefficient of the train increases by 10.74%.The head drag coefficient increases with the rainfall intensity and decreases with the vehicle speed.The aerodynamic model of high-speed train in wind and rain environment is established,and the crosswind and raindrop are simulated iteratively by wind-rain two-way coupling method.Based on this,the water film distribution and aerodynamic performance of high-speed train body under different train speeds,different crosswind speeds and different rainfall intensities are studied.The calculation results show that raindrops first accumulate on the top and windward surfaces of the high-speed train to form a water film,and as the duration of rainfall increases,the water film on the top of the train gradually flows to the leeward side.The average water film thickness of the train surface increases with rainfall intensity.In the wind and rain environment,the shear stress and skin friction coefficient of the windward side of the high-speed train are greater than those of the leeward side.When the speed and crosswind speed are constant,the aerodynamic coefficient of the head car increases with the rainfall intensity.Compared with rainless environment,when the rainfall intensity is 500mm/h,the lift coefficient increases by 14.57% and the nodding moment coefficient increases by 9.95%.Based on the multi-body system dynamics theory of high-speed train,the dynamic model of the head car is established.The aerodynamic load of high-speed train under wind and rain environment is applied to the dynamic model of the head car,and the dynamic performance of high-speed train under different rainfall intensity,different crosswind speed and different train speed is analyzed.The calculation results show that the safety index of high-speed train operation increases with the train speed,crosswind speed and rainfall intensity.Compared with the rainless environment,when the rainfall intensity is 500mm/h,the derailment coefficient,wheel load reduction rate,axle lateral force and wheel-rail vertical force increase by 3.08 %,4.24 %,62.16 % and 2.28 % respectively.Based on the DPM-VOF coupling method,this study investigated the water film distribution on the body of a high-speed train in rainfall environment.The calculation results show that when the water film thickness is below the threshold calculated by the Eulerian wall film model,the water film on the train body is modeled using the Eulerian wall film model.When the water film thickness exceeds the threshold,it transitions to the VOF approach and is modeled as a liquid phase in multiphase flow.The shear stress of water film transition to VOF liquid region is larger,and the corresponding skin friction coefficient and water film flow velocity are larger.Compared with rainless environment,when the rainfall intensity is 500mm/h,the aerodynamic drag of the head car increased by13.57%.