| High speed maglev transportation has many advantages,such as high efficiency,safety and punctuality,strong transportation capacity,comfortable and environmental,etc.It can be applied to long-distance transportation between hub cities or urban agglomerations,and also can be applied to the internal commuting of large cities or the "integration" of urban agglomerations of medium and short distance transportation.It can also fill the speed gap between high-speed rail 350km/h transportation and aircraft 800-900 km /h transportation.As high-speed maglev transportation can meet the travel needs of different groups of people,it has a very broad application prospect.In June 2020,a new model maglev vehicle with a speed of 600km/h rolled off the production line in Qingdao successfully ran on the Shanghai maglev test line,marking a major breakthrough in China’s high-speed maglev transportation technology.When the maglev train enters the tunnel at a certain speed,the air flow in front of the train head is restricted by the compressibility of the air and the annular space of the tunnel,leading to the rapid rise of the pressure in front of the train head and the formation of initial compression wave.The initial compression wave propagates along the tunnel to the tunnel mouth and generates micro-pressure wave through radiation.It can cause vibration damage and noise pollution to nearby buildings and residents.When the speed of maglev train is as high as 600km/h,the phenomenon of micro-pressure wave will be more intense.Studies show that the intensity of micro-pressure wave is proportional to the maximum pressure gradient of compression wave propagating to the exit of the tunnel.Therefore,the maximum pressure gradient of initial compression wave generated by maglev train entering the tunnel is an important factor affecting the micro-pressure wave.A hood structure at the tunnel entrance can reduce the maximum pressure gradient of the initial compression wave caused by the maglev train entering the tunnel,thus alleviating the phenomenon of micro-pressure wave.In this paper,the CFD method is used to solve the Navie-Stokes equations of three-dimensional unsteady air flow,based on the finite volume method and the overlapping grid technology,based on the effect of different types of hood structures on the initial compression wave mitigation,combined with the new 600km/h maglev train head model.By using the SST k-ω model and the all-Y + wall treatment method,the basic characteristics of the initial compression wave when a high-speed maglev train enters a tunnel without a hood structure and round expanded section hood structure with opening are numerically simulated.Compared the several kinds of hood structure(round expanded section hood structure with openings,round expanded section hood structure without openings,round equal section hood structure with openings)of the initial compression wave slow effect,finally analyzes the maglev train by enlarging section circular hole hood structure cushioning structure and train the body pressure load distribution characteristics.The research results of this paper can provide a theoretical basis for the engineering application of maglev transportation with a speed of600km/h in the future.This thesis is in the National Key Research and Development Program " Advanced Rail Transit" key special tasks "Maglev Trains/Tunnel Coupling Numerical Nimulation Research of gas dynamics behavior" and China Railway Eryuan Engineering Group Co.LTD’s project "400 ～ 600 km/h Maglev Transportation Key Design Parameters of Tunnel" funding,The main research work of this paper is as follows:1.The basic characteristics of the initial compression wave when the maglev train enters the tunnel with no hood structure at a speed of 600km/h and the hood structure with a circular opening with an expanded section are analyzed.The results show that the basic characteristics of the initial compression wave in the tunnel and the hood structure are similar,but the amplitude is different.The initial compression wave in the tunnel/hood structure has threedimensional characteristics at the early stage of formation,and the initial compression wave effect on the wall of the tunnel/hood structure near the car body is more obvious.2.The propagation characteristics of the initial compression wave in the tunnel/hood structure are analyzed,and it is proved that the three-dimensional characteristics disappear after the initial compression wave travels a certain distance forward along the tunnel/hood structure and becomes a one-dimensional plane wave.On the same section,the initial compression wave pressure and pressure gradient on the side far away from the car body are the same at different heights.On the side close to the car body,the closer it is to the ground,the greater the initial compression wave pressure and pressure gradient are.3.Compare the several different types of hood structure(round expanded section hood structure with openings,round expanded section hood structure without openings,round equal section hood structure with openings)slow down the role of the initial compression wave,the results show that such as round equal section hood structure with openings on initial compression wave pressure gradient slow work best(slow down the rate of 69.6%),The round expanded section hood structure with openings is the second one(the mitigation rate is 36.2%),and the round expanded section hood structure without openings has the worst mitigation effect on the initial compression wave pressure gradient(the mitigation rate is 36%).4.In order to round expanded section hood structure with openings as an example,the maglev train is analyzed through the structure of cushion structure in the process of pressure load distribution,the results show that the hood structure close to the body side pressure fluctuations than from the hood structure side pressure fluctuations,close to the body side of the hood structure inside and outside differential pressure maximum positive 1518.12 Pa,The maximum negative value of internal and external pressure difference is-1148.23 Pa.5.In order to round expanded section hood structure with openings as an example,the maglev train is analyzed by different hood structure in the process of train body pressure load distribution of measuring points,the results show that the maglev trains at the bottom of the car body pressure load is greater than the sides and the roof pressure load of the maglev train,this phenomenon will help maglev train above the track beam suspension;Moreover,the pressure load values at the bottom of different carriage bodies of the maglev train are all positive,while the pressure load values at the top and both sides of different carriage bodies of the train are all negative. |
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