Experimental Study on the Entry Compression Wave in a Model Tunnel

초록

High-speed trains entering a tunnel create aero-acoustic instabilities leading to a host of environmental problems; such as rattling of structures near the exit part of the tunnel and also an explicit acoustic nuisance due to the emission of micro-pressure waves. Moreover, the propagating waves hit back and forth in the walls of the tunnel creating wave induced stresses; thereby creating discomfort to the passengers inside the train car. Much of the research orientation has been towards understanding the formation process of micro-pressure waves at the exit and subsequently a lot of analysis has been devoted for their attenuation. Very little focus has been given to understand the formation process of the compression waves produced at the entrance of the tunnel. As the nose of the train approaches the tunnel entrance plane, the stationary air inside the tunnel gets compressed creating a piston effect; thereby causing the wave to propagate at the local speed of sound. A part of this wave exits from the far end of the tunnel as a weak micro-pressure wave. The remaining part tries to escape through the annular gaps between the train and the tunnel as a fluid jet. The compression wave that generates at the entrance is the very first of the successive compression waves and this emits energy at the entrance section as a monopole source of sound.