Ventilated Approach Regions for Railway Tunnels

A possible method of reducing the magnitudes of the pressure transients generated when railway trains enter tunnels at high speeds is described. Some such method will be required in the near future to avoid causing severe aural discomfort to passengers as a result of rapid changes in the ambient pressures in tunnels. It is proposed that a long continuously ventilated precompression tube should be built onto the outside of a tunnel so that the pressure build-up in the unventilated region will occur only gradually. The analysis includes both unsteady and compressible effects and a numerical solution is obtained by the method of characteristics. It is shown that very little ventilation is required and that it is better to distribute the ventilating holes evenly along the approach region than to concentrate them close to the entrance. From the passengers' point of view, the optimum situation occurs when the sudden pressure rise on the front of the train as it enters the tunnel is only slightly reduced.