Influence Of Wind Shielding Effect Of Bridge Tower On Aerodynamic Characteristics Of Vehicle-Bridge System

Bridges account for a considerable proportion of high-speed railways.Long-span bridges are affected by strong winds.There is complex three-dimensional flow around the bridge towers,and wind environment in the bridge deck is complex and changeful,which affects the safety and comfort of high-speed trains.The nature is catastrophic,and the coupling of train wind and natural catastrophic wind has an impact on high-speed trains in the area of bridge towers.Therefore,it is of practical significance to study the influence of shielding effect of the wind in the area of the bridge tower on the aerodynamic characteristics of the train-bridge system.A three-dimensional aerodynamic analysis model and a train multi-body dynamics model of a high-speed train in the area of the bridge tower are established,and the aerodynamic load mutation process of the train and the aerodynamic load coefficient of the bridge section in the area of the bridge tower in the random wind,as the train travels on a single line and intersects at a constant velocity,are analyzed.The aerodynamic response characteristics and causes of the train in the random wind field are discussed from the perspective of the flow field structure,the time domain and frequency domain characteristics of the aerodynamic load of the train,the reasons for the change of the safety coefficient of the train in random wind is analyzed the change law of the aerodynamic load of the train-bridge system,the bridge deck wind field and the safety parameters of the train are summarized.The results indicates:(1)The influence of random wind on the safe operation of trains is more significant than that of constant wind.The vorticity of the air near the train is about 1.1 times that under constant wind;except for lift,the peak power spectral density of various types of aerodynamic loads on the lead car is at least 60% higher than that under constant wind;at the same time,the degree of aerodynamic load fluctuation is more severe,resulting in the deterioration of driving safety.Taking the vehicle speed of 250km/h as an example,under random wind,the maximum value of the safety parameter of the leading vehicle is at least 3.12% higher than that of constant wind.(2)With the increase of the average wind speed of random wind,the driving safety deteriorates.With the increase of the average wind speed of random wind,the driving safety deteriorates.The disordered distribution of vorticity in the air around the first carriage and on the train surface increases,and the change of aerodynamic load in time domain and frequency domain is more intense.(3)In the random wind,the intersection has a significant impact on the aerodynamic load of the train,and attention should be paid to the safety of the trains in the process of moving away from each other.During trains pass at the same speed,in the random wind field,the turbulent kinetic energy of the measurement points,is three orders of magnitude higher than that in the constant wind condition,and the vortex distribution near the train is also denser,which amplifies the instability of the aerodynamic load;the maximum peak value of pressure power density at the nose of the leading vehicle under constant wind is near 1.25 hz,which is higher than that under constant wind condition and single line driving condition;when the trains rendezvous,the derailment coefficient and wheel load reduction rate begin to exceed the limit from 1.3 seconds to 1.4 seconds.(4)The aerodynamic responses of the first carriage and bridges are consistent.In the random wind,the changes of aerodynamic load of the first carriage and the aerodynamic coefficient of the bridge are similar.Both of them increase in the fifth or sixth stage of the process of the change of the wind speed in the random wind field.