Numerical Investigations On The Pressurewaves Generated By A High-speed Trainpassing Through A Tunnel

The operating and designing speeds of a morden high-speed train exceeded 0.3and 0.5Ma respectively.With the increase of train speed the aerodynamic problems of train/tunnel system become more serious and important.When a high-speed train nose entering a tunnel,a compression wave is generated,which propagates along the tunnel at nearly a sound speed.When the train's tail entering the tunnel,similar aerodynamic phenomenon generates an expansion wave.These pressure waves propagating along the tunnel and being reflected at both ends of the tunnel give rise to large “pressure transients” on the tunnel and train's surfaces,result in passenger's aural discomfort.Further,a small part of the energy of the compression wave radiates out of the tunnel as it arrives at the tunnel exit,then causes an impulsive noise called “micropressure wave”.The strength of the micropressure wave is proportional to the temporal pressure gradient of the compression wavefront.In some cases,the micropressure wave could be very loud to induce a serious environmental problem.During the past decades,a lot of efforts focused on the transient pressure and the temporal pressure gradient of the compression wavefront.The previous work established a simplified theoretical model,to forecast the strength of the compression wavefront,and simulate the propagation and reflection of the pressure waves inside the tunnel;proposed some criteria for the passenger's aural comfort;designed a mathematical model to express the relationship between the pressure transients on the train's outer surface and inside the train;provided some parametric analysis on the initial compression wavefront generated by a normal tunnel entrance.In viewer of that most of the previous work are based on case studies,the research on “the transient pressure” or on “the compression waves generated by some complex tunnel entrances,such as the inclined portals,unvented and vented hoods”,are still far from sufficient.The main purpose of the present work is to provide a systematic research on the mechanism and rules of the influence of some physical,geometrical parameters on the transient pressure and temporal pressure gradient of the initial compression wavefront.The main contents are as follows:(1)The numerical models of “train/tunnel aerodynamics” are designed and validated.Detailed analyses are conducted and concluded on the numerical error,and the range of validity of individual numerical models for different engineering cases.(2)The numerical investigations are conducted on the aerodynamic performances of inclined portals,unvented and vented hoods.The relationships between the“maximum temporal pressure gradient of the initial compression wavefront” and some physical,geometrical parameters are studied and concluded,such as the train speed,the shifting of the train away from the tunnel median line,the blockage ratio of train to tunnel,the inclination angle of tunnel portal,the section ratio of hood totunnel,the hood length,the location and area of ventilation window,etc..(3)The numerical investigations are conducted on the transient pressure.The fluid mechanism of the pressure transients on the tunnel and train's surfaces are revealed.The evaluation of passenger's aural comfort are provided based on a large number of numerical cases.The influences of some physical,geometrical parameters on the pressure transients inside the train,are investigated and concluded,such as the train speed,the blockage ratio of train to tunnel,train and tunnel lengths,and the coefficient of train's sealing performance,etc..