High Speed Railway Ballasted Track Aerodynamics Research Based On Wind Tunnel Test And CFD Simulation

Ballast flight obsesses the ballasted high-speed railway,and its mechanisms are not well understood.This phenomenon not only limits the operational speed,but also causes impact and fatigue damage to track and train structures,further endangering operational safety.The present paper put forward a wind tunnel test and CFD simulations to study ballast flight mechanisms and ballasted track aerodynamics.Based on high speed ballasted track design and ballast material standards,a 1:1 scale half ballasted trackbed model which is set up to investigate the influential factors and their impacts on the train and ballast aerodynamics.And standard size ballast,small size ballast and light ballast are screened out to evaluate the movement of different ballasts under the wind load.Experimental results are analyzed for a deeper understanding of ballast flight related to track bed aerodynamics and track bed cross section details.Systematic analysis of the static pressure in different positions was presented to evaluate airflow around the track surface.In the meantime,k-? SST two-equation turbulence model were used to validate experimental results.Results reveal that under the uniform flow,the wind in the center of the ballast bed has higher but reletavely stabler wind pressure and speed.Wind pressure between sleepers changes from negative into positive one,and sleeper end and crib produces more pressure.Rail and crib result in large fluctuation of wind pressure and cavity vortex.The less shoulder ballast height and crib top decrease the probability of ballast flight.The ballasts which are light or lying on the sleeper surface are more easily to move.And ballast track bed which sprayed polyurethane glue on the surface can totally avoids ballast flight.To evaluate airflow around the train and track,k-epsilon realizable viscous model is adapted together with a sliding mesh technique,to establish CRH3 train and ballasted track bed numerical models of a single train running in open air at speed of 250 km/h,300 km/h,350 km/h and 400 km/h,respectively.The main research conclusions are summarized as follows:1.Train head,train tail and bogie area has large fluctuation of wind pressure and speed,where has a high probability of ballast flight.The pressure and wind velocity above track has strong variations before the train nose passing or after the train tail going by.However,they are relatively stable in the central region.2.The key aerodynamic factor of ballast flight is train speed.Increasing train speed,the peak value and the fluctuation of wind pressure becomes larger.When the train speed is above 250 km/h and train speed is increased by 100 km/h,the peak value of wind pressure is double.3.The ballasted track bed structural form is one of important factors affecting the ballast flight.The pressure increases with the higher shoulder ballast and the lower crib top,but reducing crib top significantly decreases the probability of ballast particles moving onto the sleeper surface.Peaked shoulder ballast pressure fluctuation is small,which is more effective to prevent ballast flight.