چكيده به لاتين
Besides improving transportation industry, attention to passenger safety and comfort has been of great importance. Regarding passenger trains and according to vast improvement of railway industry across the world, high-speed railway fleet has become more and more important. One of the most important technical challenges in high-speed trains is scientific, practical investigation of aerodynamic of such trains. Problems such as derailment because of lateral forces, engine improvement of these vehicles, speed increase of trains, and other cases all show how important aerodynamic study is in high-speed trains. When a train enters a tunnel, the importance of these topics multiply; because in this condition pressure and expansion waves produced by piston phenomenon impose strong strikes on both train and tunnel structure. This phenomenon influences tunnels and stations air conditioning, and causes air flow in the tunnel’s air conditioning system. In constructing a tunnel for high-speed trains, the pressure waves and the forces followed by the waves must be considered, and all of these problems are related to piston effects caused from the entering train. Because of the importance of the subject, the parameters which are effective in this phenomenon and the studies which are accomplished till now are investigated and are discussed. In addition, in the present study, for completing prior researches, the phenomenon is studied in different states of train’s velocity and tunnel’s length. For improving the destructive effects of the piston phenomenon, some shafts are embedded and the effects of pressure waves are presented. Results show that by increasing train’s velocity or increasing tunnel’s length, the pressure wave become stronger along the tunnel; thus, shafts are embedded at the outset, middle, and end of tunnel with the aim of decreasing the wave’s amplitude. The numerical method, which is used in the present study, uses sliding mesh techniques in computational fluid dynamics (CFD). It is worth to mention that this study is accomplished with the aim of investigating pressure waves for Tehran-Qom-Esfahan high-speed railway line which is going to move by 350 km/h. One of important subjects related to constructing a high-speed tunnel is calculation of produced pressure and the induced forces followed by that from piston effect at the outset of tunnel. In some situations, it is possible that this parameter causes damage to train or even reversal and derailment of train. Also, according to high velocity of the train at the entrance of tunnel, air pressure changes and air velocity changes in the runnel are considered.
