Aerodynamics Research On Two High-Speed Trains Passing Through In Tunnel

With the rapid development of high-speed railway, the higher requirement of railway line technology standard results in more tunnels appearing. Air pressure around the train changes dramatically in short time due to limited space constraint of tunnel and causes increasing driving resistance, discomfort for passenger, the micro-pressure wave in tunnel exit, etc. The transient pressure induced by two high-speed trains passing through in tunnel is more violent than that by a single train passes a tunnel which leads to more serious and more complicated aerodynamics in transient pressure, air drag force, air side force, micro-pressure wave, aerodynamic noise and so on. It is quite necessary to do the profound and comprehensive aerodynamics research of two high-speed trains passing through in tunnel.Based on three dimensional unsteady N-S equation of compressible viscous fluid and the two-equation k～εturbulent model, pressure and aerodynamic forces variation induced by two high-speed trains passing through in tunnel were calculated numerically by means of the finite volume method. With multi-case computation, the paper analyses pressure and aerodynamic forces variation induced by two high-speed trains passing through in tunnel due to the effects of train velocity, tunnel length, train composition length, tunnel cross-sectional area, location of two trains meeting, obtains the relationship between aerodynamics and influence factors and gives recommendations. Also, the paper studies tunnel portal effect on transient pressure and researches the impact of buffer structure on aerodynamics for two high-speed trains passing through in tunnel.The results show that transient pressure induced by two high-speed trains passing through in tunnel certainly lies on propagation and superposition by compression wave and expansion wave of tunnel portal and air pressure pulse as trains passing and is under the influence of various elements. The transient pressure has a relation to train velocity in power function with the power being greater than 2 and decreases slightly with the increase of tunnel length. The amplitude of pressure variation is larger when tunnel length is twice to four times as long as train composition length. The max pressure variation is more than body pressure limits when two trains at the speed between 350kmph and 400kmph pass a tunnel with 100m2 cross-sectional area and it is significant to reduce the pressure variation via increasing tunnel cross-sectional area. The most dangerous condition is that the two trains meet in the middle of tunnel for there being the max pressure variation. The air drag force variation of train and the transient pressure variation on the train body for two trains passing through in tunnel are consistent, which are much more than that induced by two trains passing through in the open air or a single train passing a tunnel at the same speed. The air side force and the air lift force of train with train velocity in power function with the power there being two are mainly related to air pressure pulse and are not related to tunnel length, tunnel cross-sectional area and location of two trains meeting. Buffer structure is an effective measure to decrease pressure and air drag force variation.