Propagation characteristics of compression wave in a high-speed railway tunnel

A compression wave is generated due to a piston effect as a high-speed train enters a railway tunnel. The compression wave propagates ahead of the train at local speed of sound. As it propagates along the tunnel, the wall friction causes the wave front to distort during this process. The distortion of the wave could be distinctly characterized by the peak over pressure attenuation, waveform steepening, and wavelength widening. The characteristics of the propagating wave strongly depend on the friction factor, train to tunnel blockage ratio, and train speed. The propagation characteristics of compression wave can have a great impact on the train aerodynamics as well as the micro-pressure wave emitted from the exit of tunnel. Hence, it is extremely important to understand the propagation characteristics of a compression wave in a railway tunnel. In the current study, one-dimensional Euler equations with steady and unsteady friction considering the roughness of the tunnel wall have been solved using the method of characteristics. The effect of the blockage ratio and train speed is studied here in detail. The obtained data depicts non-linear distortion of the compression wave to be noticeably higher for the case of higher blockage ratio. The peak over pressure attenuation decreases along the tunnel length, and the waveform steepens as train speed is increased. The critical length of a tunnel where the steepening ratio reaches a maximum value is determined from the case study conducted. The critical tunnel length decreases as train speed is increased.