The Effects of Side Branches on Compression Waves Propagating in High-Speed Railway Tunnels

Abstract

According to the theory of finite amplitude sound waves, a one-dimensional compressible unsteady non-homentropic flow model, and the method of characteristics based on the average parameter method are applied to calculate the propagation of entry compression waves in a tunnel, in which the strength of the entry compression wave mainly affects the magnitude of the micro-pressure wave. In addition, acoustical principles are used to simulate the effect of side branches in the tunnel on the sound wave to elucidate the distortion of the waveform of the compression wave. A real-world comparison shows that the programs presented correctly reveal the distortion of the compression wave in the tunnel. After validation, the effects of the number, location, and depth of the side branches are studied in detail. The results show that any change in the parameters of a single side branch has almost no effect on the distortion of the waveform of the compression wave. An increase in the number of side branches, however, does make their effect more significant. This is due to an increase in streaming and reflections which substantially reduce the pressure gradient of the compression wave arriving at the exit portal of the tunnel.