Studying On The Influence Of The Stepwise Hood For The Aerodynamic Effect Of Tunnel

When the initial compression wave is generated before the high-speed train enters the tunnel and spreads to the exit end of the tunnel,when the intensity of outward radiation is large enough,the micro-pressure wave at the entrance is formed,which has a serious impact on the surrounding environment of the tunnel and the residents.When the train passes through the tunnel,it forms the pressure wave of the tunnel,which is introduced into the carriage.Therefore,the numerical simulation of the aerodynamic effect of the train through the tunnel has practical significance and practical value.A stepwise hood at the tunnel entrance can effectively increase the thickness of the initial compression wave front,increase the time of pressure curve rise,reduce the peak pressure gradient,and slow down the aerodynamic effect inside and outside the tunnel.Buffer structure in a variety of forms,this article is based on three dimensional,compressible,unsteady Navier-Stokes equation and using sliding mesh technology realizes the train and the relative motion of the tunnel,relying on the Beijing-Shanghai High-speed railway Xikema no.2 tunnel,the ladder type cushion structural parameters changes inside and outside the influence of the aerodynamic effect of the tunnel,mainly do the following:(1)Establish a three-dimensional numerical model of the stepwise hood,adopt the sliding grid technology to simulate the aerodynamic process induced by high-speed trains through tunnels,and analyze the buffer mechanism.(2)By changing the length lh,order n,section ratio of each order and inlet area AE of the stepped buffer structure,the initial compression in the tunnel was simulated and swept to its pressure gradient,the buffering effect was analyzed,and the influence of the structural parameters of the stepped buffer structure on the aerodynamic effect of the tunnel was studied.(3)The tunnel hood of equal length steps and equal ratio steps were respectively studied,and the buffering effect was analyzed by comparing the initial compression and its pressure gradient.Though comparative analysis,it is found that the stepwise makes the pressure rise slowly in the tunnel.It also can reduce the influence of aerodynamic effect.Increase the length,number of steps and sectional area of of buffer structure can increase the effect of aerodynamic.Equal length and equal ratio of stepwise hood structure can change the effect of hood.