Study On The Alleviation Of Hood With Multiple Windows On Pressure Fluctuation Characteristics Inside And Outside The Tunnel Induced By High Speed Maglev Train Passing Through The Tunnel

When a high-speed train enters a tunnel,on the one hand,an initial compression wave is formed at the front of the train.The initial compression wave propagates to the exit of the tunnel at local sound speed.When the compression wave propagates to the exit of the tunnel,a part of it radiates out of the tunnel in the form of a pulse wave at the exit of the tunnel.The pulse wave is called a micro-pressure wave,and the magnitude of the micro-pressure wave is approximately proportional to the cube of the train speed;on the other hand,the low frequency pulse wave radiated directly from the tunnel entrance can be observed near the tunnel entrance,which is called the tunnel entrance wave.The tunnel entrance wave is also approximately proportional to the cube of the train speed.Micro-pressure wave and the tunnel entrance wave belong to infrasound wave category,which will have a serious impact on the environment of buildings near the tunnel entrance.When the speed of high-speed maglev train reaches 600 km/h,the aerodynamic problems will become more serious.When the speed of railway operation increases from 300 km/h to 600 km/h,for the same tunnel section and train,the micro-pressure wave at the tunnel entrance and the tunnel inlet wave are about 8times as much as the original.How to reduce and take measures to solve the aerodynamic effect in the tunnel is the fundamental problem that must be solved in the high-speed maglev railway tunnel.At present,there are two main ways to mitigate micro-pressure wave and the tunnel entrance wave.One is to optimize the head design from the train aspect;the other is to install hood at tunnel entrance.This paper mainly studies the installation of hood at the entrance of tunnel to alleviate aerodynamic effects.Based on three-dimensional,unsteady Reynolds-averaged N-S equations and SST k-?two-equation turbulence flow model,the relative motion between train,hood and tunnel is simulated by overset mesh technique.The validity and rationality of the meshing method and the numerical calculation method are verified by the model experiments of Japanese ellipsoidal train model.Taking the high-speed maglev tunnel with cross-section areas of 140 m~2 and the high-speed maglev train in China as the research object,this paper simulates the initial compression wave and the tunnel entrance wave generated by the maglev train enters hood with multiple windows and hood with no window,reveals the formation mechanism and variation characteristics of the initial compression wave and the tunnel entrance wave,and analyses the effect of the windows of hood on the initial compression wave and the tunnel entrance wave.The main conclusions are as follows:(1)When the compressed wave induced the head car of maglev train at the maximum change rate of cross-sectional area enters hood propagates to the pressure monitoring point in the tunnel,the pressure gradient is the largest.(2)When the head nose of the maglev train enters the hood,the initial compression wave is generated.After 3.75 times of the distance(60m),the initial compression wave changes from"three-dimensional wave"to"one-dimensional plane wave".(3)The peak pressure gradient of the initial compression wave in the hood with multiple windows is 67.13%slower than that in the hood with no window,and the time of obtaining the peak pressure gradient is 20.44%later than that in the hood with no window.In terms of the maximum compression wave,the hood with multiple windows is 5.68%larger than in the hood with no window.(4)Negative pressure pulses are generated when the head enters the hood and positive pressure pulses are generated when the tail enters the hood;the tunnel entrance wave has directivity and attenuation,and the peak value of the tunnel entrance wave is inversely proportional to the distance;the tunnel entrance wave is asymmetric in the double-track tunnel.(5)As for the effect of the windows of hood on the tunnel entrance wave,the monitoring point located in the section of open line is not affected by the windows.At the monitoring point above the entrance of hood,the negative peak value of hood with multiple windows is41.2%-50.8%lower than that of hood with no window.The positive peak value of the hood with multiple windows is 44.4%~62.1%lower than that of the hood with no window;at the monitoring point above the hood,the negative peak value of the hood with multiple windows is 50%~57.7%lower than that of the hood with no window,and the positive peak value of the hood with multiple windows is 78%~98.5%lower than that of hood with no window.