Numerical Study On Pressure Waves Produced By Trains In Complex Tunnel

With the increasing of train speech, the aerodynamic problems including the tunnel pressure waves have become more and more important, seriously affecting the high-speed, comfort, reliability, economy and security of railway. Due to the characteristics of mountainous terrain and high ratio of tunnel to line, the problem of tunnel pressure waves has become particularly prominent. Besides, with the rapid expansion of urban subway in China, there are obvious problems of tunnel pressure waves. Many scholars have devoted to the related researches at home and abroad, but there are a fewer systematic researches on the pressure waves when the train passes through a longer and more complex tunnel.Based on the numerical method, this paper takes the tunnels of high-speed railway and subway as the research objects and researches the problem of tunnel pressure waves. The main contents are summarized as follows:(1) According to the one-dimensional flow characteristics of the air flow induced by the train passing through a tunnel, the numerical methods are proposed, which can be used to calculate the tunnel pressure waves under the conditions of(multi-)shafts,(multi-)cross passages, and the variable cross-section areas of the tunnel.(2)The influence, acting on the tunnel pressure waves by shafts is also studied. The research results are reflected in three aspects. Firstly, the reasonable arrangement of shafts is helpful to reduce the maximum variation of the pressure on train and in tunnel when the train passes through the tunnel. And in a short tunnel, the external pressure variation of single train is more easily affected by the position of the shaft. Even if the same position, it also has different effect on different points in the tunnel. Besides, the effect of cross-sectional area on the external pressure variation is related to shaft position. But to relief the pressure, it is better to choose the smaller area. Lastly, in the tunnel of 10000 m, the number of shaft has no obvious effect on the pressure of the train and the tunnel, but the pressure variation in the vicinity of the tunnel is decreased obviously.(3) The study also shows that the cross passage has an influence on pressure waves produced by single train or two trains crossing in the tunnel. It is found that any position of the cross passage is good for reducing the maximum pressure amplitude when single train passes through the tunnel. Even if in the same position, the influence on different points is not the same. In addition, when the distance from the position to the entrance is less than the critical distance, the cross-section area of the cross passage has less influence on the pressure amplitude by single train passing and two trains crossing in the tunnel, but when it is more than the critical distance, the pressure amplitude becomes greater with increasing the cross sectional area. It is advantageous to reduce the pressure amplitude when the distance is less than the specific value.(4) The characteristics of pressure waves in high speed subway are studied. The result shows that under the condition of the shield diameter 6m,the change of train’s outer pressure exceeds the pressure comfort requirements when the train enters into a simple tunnel at full speed of 120km/h, while that meets the requirement when the speed reaches 120km/h after starting. And it is also found that the pressure fluctuation is increased when the train passes through the shaft and the cross passage. In order to reach the requirement of the pressure comfort, it is unrealistic to only increase the tunnel cross-sectional area; it is also need to improve the airtightness of the train.(5)Through analyzing the characteristics of pressure wave, the paper concludes that the pressure wave consists of a group of feature waves. Based on this, the length formula of characteristic tunnel is derived relative to the pressure values in the tunnel. At the same time, the fast estimation method is presented, and the paper tries to apply it for estimating the tunnel pressure waves in shaft. The application proves that the method is reasonable, but it does not consider the effect of fluid flow, so the result cannot accurately reflect the deformation of the pressure wave.