Study On The Pressure And Air Tightness Of High-speed Trains Running In Tunnel

With the rapid development of high speed railway,the train speed is continuous increasing,the corresponding aerodynamic problems have become increasingly prominent,and a higher requirement is put forward for the design of carbody strength and air tightness of the train coach.In this paper,the pressure and air tightness of high-speed trains in tunnel were studied by using numerical simulation method.The conclusions are listed as follows:Firstly,based on the three-dimensional unsteady and compressible N-S equation,threedimensional sliding finite element models of two identical high-speed trains passing each other with uniform velocity in the most unfavorable tunnel under five different train formations(including eight,ten,twelve,fourteen and sixteen train formation)were built by using commercial software ICEM CFD,respectively,and the corresponding aerodynamic performance was conducted by using CFD software FLUENT.The results indicate that between eight-section and sixteen-section the amplitude of the train surface pressure is increased with the increasing train formation,except for the nose-tip position of the head car and the tail car.Secondly,the train surface pressure of a typical eight-section high-speed EMU passing through tunnels with three different blockage ratios was studied.The results indicate that the amplitude of the train surface pressure is increased monotonously with the increase of blockage ratio,except for the nose-tip position of the head car.Thirdly,the simplified static leakage numerical model was built based on the actual structure of the train coach,and the theoretical formula of the relationship between the internalexternal pressure difference and the pressure descending time and equivalent leakage area was deduced based on fundamentals of hydromechanics.Then the theoretical formula was validated by using test method and numerical simulation method,respectively.The results indicate that the theoretical formula is appropriate to describe the change of the internal-external pressure difference,and the correction factor ?=0.8 was obtained by fitting the numerical result based on the theoretical formula.Forthly,based on the air tightness index and the theoretical formula of the relationship between the internal-external pressure difference and the pressure descending time,limiting cases of the change of the internal train pressure under different external train pressure conditions were obtained,and then the change trend of the maximum equivalent leakage area was obtained for different tunnel conditions.The results indicate that the maximum equivalent leakage area of the middle train coach is decreased with the increasing train formation for two identical high-speed trains passing each other with uniform velocity in the tunnel,and the maximum equivalent leakage area of the middle train coach is decreased with the increase of blockage ratio for a high-speed train alone passing through tunnels with three different blockage ratios.Furthermore,by comparing the condition of a high-speed train alone passing through the tunnel with the condition of two identical high-speed trains passing each other with uniform velocity in the tunnel,it is founded that the requirement of air tightness for the condition of two identical high-speed trains passing each other with uniform velocity in the tunnel is significantly higher than that for the condition of a high-speed train alone passing through the tunnel.