High Speed Rail Tunnel Aerodynamics: Transient Pressure and Loadings on Fixed Tunnel Equipment

摘要

Trains entering tunnels at high speeds can generate highly transient air velocity and pressure fields inside the tunnel, from time of entry until well after they leave the tunnel. The parameters affecting the induced velocity and pressure fields include train speed, train to tunnel blockage ratio, train to tunnel length ratio, shape of train nose and tail, and the number, spacing intervals and area of pressure relief shafts. Compression waves continuously induced by the train nose propagate along the tunnel at the speed of sound, and compress and accelerate air in front of it, until they reach the exit portal. These will then reflect as re-. fraction waves, interact with other travelling waves and set up complex micro-pressure wave patterns and airflows. Some of the rapid pressure changes can create aural discomfort for passengers. The designer has to ensure that the cross sectional area of the tunnel is large enough so as not to exceed these maximum pressure thresholds. In cases where the tunnel cross section cannot be met, other engineering solutions like the provision of pressure relief shafts are considered. Apart from provision of pressure relief, a separate mechanical ventilation system is needed to provide- a safe environment during an emergency fire incident, as well as a comfort for passengers in a train congestion scenario. While large axial fans in supply and extract configuration have been the traditional solution, other approaches are possible like Saccardo nozzles and jet fans, as used in the Channel Tunnel Rail Link (HS1). Thus the issue of transient forces and moments on installed e-quipment such as fans, signs, brackets and panels in high-speed tunnels are discussed, drawing on the experience of HS1.