Study On Aerodynamic Effects Of 400 Km/h High-speed Trains Passing Through Tunnels

The aerodynamic effects of high-speed trains passing through the tunnel will adversely affect the safety of train operation,the comfort of the occupants in the train,the safety of the occupants in the tunnel,and the environment near the tunnel exit.These effects will be further exacerbated as the speed of trains increases.Therefore,it is crucial to study the aerodynamic effects and mitigation measures of high-speed trains with higher speed classes passing through tunnels.Based on the theory of computational fluid dynamics,a three-dimensional numerical calculation model of a 3-group high-speed train passing through a tunnel is established,the basic laws of the aerodynamic effect of the train passing through the tunnel are studied,and the internal pressure and air tightness parameters of the high-speed train are matched and designed.The influence of typical buffer structure on the aerodynamic effect of the tunnel is studied,and a new buffer structure reducing the aerodynamic effect of the tunnel is designed.Firstly,the variation law of the basic aerodynamic effect of the train passing through the tunnel and the influence of the speed grade on it are studied.The results show that the compression and expansion waves propagating and transformed in the tunnel largely determine the aerodynamic effects of the train passing through the tunnel.Increasing the speed rating significantly worsens the aerodynamic effects of the train as it travels through the tunnel.Compared with 350 km/h,when the high-speed train passes through the most unfavorable length tunnel at 450 km/h,the maximum negative pressure of the side window of the train increases by 64.9%,the aerodynamic resistance in the tunnel increases by 62.0%,and the amplitude of micro pressure wave increased by 127% at 20 m from the tunnel exit.Secondly,the propagation model between inside and outside of the train of when it passing through the tunnel is established.The variation law of the pressure inside the train is studied,and the matching design of the pressure inside the train and air tightness parameters of the train is carried out.The results show the overall variation trend of the pressure inside the train is similar to the surface pressure of the train,but there is a time delay.With the increase of the speed and the decrease of the dynamic sealing index,the pressure change in the train increases in a same period.When the train runs at a constant speed,the minimum limit of the dynamic air tightness index of the head car meeting the standards of ≤ 500 Pa/1 s and ≤ 800 Pa/3 s of pressure change in the train is 4.5～6.5 s,the minimum limit of the air tightness index is 4.6～7.2 s for middle and tail train.When the dynamic sealing index of the train is bigger than 7.2 s,all the carriages at each speed level can simultaneously meet the standard requirements of ≤ 500 Pa/1 s and ≤ 800 Pa/3 s of pressure changes in the vehicle.Then,the influence of different typical buffer structures on the aerodynamic effect of the train passing through the tunnel is studied,and the mitigation effect is evaluated in combination with relevant standards.The research results show that the typical buffer structure has no obvious influence on the variation law of aerodynamic effects,but it will advance or delay some critical moments of aerodynamic effects which produced by it to a certain extent,and it will also reduce the variation amplitudes of various aerodynamic effects except for the train wind velocity.Among the four typical buffer structures,the equal-section enlarged buffer structure has the best mitigation effect.Some typical buffer structures can meet the standard of micro-pressure wave amplitude at 20 m from the tunnel exit,but all typical buffer structures cannot meet the standard of micro-pressure wave amplitude at 50 m from the tunnel exit.Finally,four new buffer structures are designed on the basis of typical buffer structures,the influence of different new buffer structures on the aerodynamic effect of trains passing through the tunnel is studied.The results show that compared with the typical buffer structure,the new buffer structure has a better mitigation effect on the aerodynamic effect of the highspeed train tunnel passing through the tunnel reduced.Among the four new buffer structures,the hat brim oblique cut equal cross-section enlarged buffer structure(type I buffer structure),equal ring oblique cut equal cross-section enlarged buffer structure(type II buffer structure)and double equal cross-section enlarged buffer structure B(type IV buffer structure)can meet the micro air pressure wave amplitude standards at 20 m and 50 m away from the tunnel outlet,but the mitigation effect of type I buffer structure is better.