Numerical Studies On The Tunnel Hood Structures To Attenuate The Initial Compression Waves And The Micro Pressure Waves Of The High-speed Maglev Train

With the 600 kph maglev train rolling off the production line in Qingdao,the problem of tunnel micropressure wave facing it can not be ignored.When the maglev train passes through the tunnel,the compression wave will be generated when the front of the train enters,and the expansion wave will be generated when the rear of the train enters.The compression wave and the expansion wave will propagate reciprocately between the entrance and exit of the tunnel and constantly overlap,resulting in a complex pressure wave system in the tunnel.In addition,the initial compression wave generated when the train head breaks into the tunnel will radiate outward to the tunnel exit and produce micro-pressure waves,which will affect the environment outside the tunnel.When the micro-pressure wave is large enough,it will produce sonic boom phenomenon and seriously affect the life of surrounding residents.To solve this problem,scholars at home and abroad have carried out a lot of research on the optimization of train head shape,tunnel section and buffer structure by using real car experiment,scale model experiment,spin body model experiment and numerical simulation.At present,in domestic engineering practice,the opening form of buffer structure at tunnel inlet is relatively simple,but with the continuous increase of train speed,similar buffer structure can not meet the minimum requirements of micro-pressure waves outside the tunnel.At present,most scholars are carrying out research on reducing the initial compression wave pressure gradient by changing the opening type and opening rate of buffer structure,but there are few studies on its mitigation mechanism.The problem of micro-pressure wave is still a major problem to be solved in the commercialization process of maglev trains.In this paper,the three-dimensional compressible unsteady flow Navi-Stokes(N-S)equation and SST k-ω turbulent flow model are adopted,and based on the overlapping grid method and the finite volume method,the calculation model of high-speed maglev train entering the tunnel is established by taking the maglev train running at 600 km/h as the research object.Firstly,the mechanism of hood reducing initial compression wave and micro-pressure wave is analyzed through the gyrocomponent model,and relevant suggestions for opening holes are put forward.Then,according to the conclusions of mechanism study and the opening way of hood,the maglev train with two sections is adopted for verification study.The main contents are as follows:(1)Based on the rotating train model,the effects of the opening position of hood on the flow field characteristics of train-tunnel coupling system and the initial compression wave of tunnel are studied;The influence law of opening position on initial compression wave is summarized and the mechanism of initial compression wave reduction caused by large opening hood with enlarged section is discussed;The suggestion of opening hood at tunnel inlet is put forward.(2)Based on the rotating train model,the flow field characteristics of compression waves in the exit hood and the slowing effect of the hood on microbarometric waves are studied;A new type of baffle hood is proposed,which can slow down the pressure amplitude of microbarometric wave more effectively than that of open hole hood.It is concluded that when only the buffer structure at the tunnel entrance is set,the initial compression wave pressure gradient reduction rate of maglev train bursting into the tunnel can reach 50%,the micropressure wave amplitude reduction rate of 20 m outside the tunnel can reach 30.5%,and the reduction rate of 50 m is 31.0%.When only the buffer structure at the tunnel exit is set,the amplitude of microbarometric wave produced by maglev train passing through the tunnel can be reduced by 36.1 at 20 m and 31.0% at 50 m.(3)On the basis of the mechanism study above,aiming at the problem of microbarometric waves caused by the maglev train passing through the tunnel at 600 km/h,the mitigation effects of three hoods on the initial compression and microbarometric waves were investigated;It is concluded that when hood is set at both inlet and outlet of the tunnel,the mitigation rate of micropressure wave amplitude outside the tunnel is about twice that when hood is set only at inlet or outlet.It is concluded that when buffer structure is set at both inlet and outlet of the tunnel,the mitigation rate of micropressure wave amplitude outside the tunnel is about twice that when buffer structure is set only at inlet or outlet.When buffer structures are installed at the tunnel inlet and outlet,the reduction rate of microbarometric amplitude of maglev train passing through the tunnel is 68.7% at 20 m and 65.3% at 50 m.