Open-end Correction on the Compression Waves Emitted from the Exit of a High-speed Railway Tunnel

초록

Compression waves generated in a railway tunnel propagate at sonic velocity and emit from the exit as a weak pulse known as Micro-pressure wave (MPW). However, the flow phenomena do not end at the physical boundary of the tunnel. Owing to the finite wavelength of the compression wave (20~30 hydraulic diameter distance), only a part of the wave energy reflects from the duct exit. The remaining part of the wave reflects back into the duct as an expansion wave from a certain distance beyond the tunnel exit. Thus, there exists a focal point outside the tunnel which the expansion wave encounters to re-enter into the duct. This focal point is customarily the imaginary end of the tunnel which is termed as ‘open-end’, and the corresponding distance from the tunnel exit to this imaginary end is known as the ‘open-end correction’. The reflected wave causes pressure transients inside tunnel that result in train car fatigue and discomfort to passengers seated inside. Therefore, it is necessary to understand the reflection process and thereafter predict the magnitudes of coefficient of transmission and reflection.