Study On Aerodynamic Performance Of High-Speed Trains In The Tunnel

As the development of modern high-speed railway, the speed of the train becomes faster and faster, and the aerodynamic problem of trains when travelling in tunnels becomes more and more severe. Under the high-speed condition, especially when combined with other conditions, for instance, passing through a series of tunnels, passing through a series of tunnels in crosswind, two trains passing against each other and etc., the more complex loads will exert on the train, which will worsen the comfort and safety of the train, and the environment alone the railway will also be affected. Therefore, the development of the train confronts a dilemma. In one hand, speeding-up is an urge problem of modern land-based transportation tools, in the other hand, the higher the speed, more dangerous the train will be. As a consequence, for the development of modern transportation tools, it is significant and meaningful to find a method to speed up a train and simultaneously avoid travelling under the severe conditions. In this paper, CFD software and SIMPACK are coupled to model several conditions, e.g., a single train travelling through a single tunnel, a single train travelling through a series of tunnels, a single train travelling through a series of tunnels in crosswind, two trains passing against each other in a tunnel and a train travelling in a vacuum tunnel. The aerodynamic characteristics of the trains under these conditions are studied and several conclusions can be drawn.1. Travelling in tunnels:a. The aerodynamic property of the train is different between travelling in a long tunnel and in a short tunnel. Due to the existence of an overlapping zone of Mach wave, the variation of surface pressure of the train is unique.b. The aerodynamic performance of the train when travelling in a series of tunnels is similar with that of the train when travelling in a single tunnel.c. The more carriages the train has, the larger the difference of pressure wave acting on different carriages is, and the higher the pulsation frequency of aerodynamic force of the last carriage is. The number of carriages will basically have no effect on the first carriage of the train.d. When travelling through a series of tunnels in crosswind, the train subjects to the combined effects of Mach wave induced by crosswind and the train itself, the surface pressures of the train differ greatly from travelling without crosswind. When entering in crosswind region, the lateral forces increase rapidly and the safety of the train is highly worsen.e. In the condition that two trains pass against each other in the tunnel, the effects of Mach wave double. The fluctuation of pressure induced by passing is relatively small in this condition. 2. Travelling in vacuum tunnela. When the train starts to move in a vacuum tunnel, the Mach wave generated will be transferred forward and backward as that induced by piston movement.b. The aerodynamic forces of the train are proportional to the cube of the tunnel pressure and the speed of the train, also it can be related to the block ratio of the tunnel.