Computational Study on the Characteristics of Entry Compression Wave in Flared and Unflared Tunnels

초록

High-speed trains entering a tunnel induce a series of pressure waves that propagate at the local speed of sound. These waves propagate down to the exit of the tunnel as a micro-pressure wave causing a booming noise i.e. a distinct aural discomfort and are strong enough in amplitude to rattle nearby structures at the exit part of the tunnel portal. These waves also cause uneasiness for the traveling passengers inside the train car due to the pressure induced stresses, as the wave propagates inside the tunnel. Researchers have dedicated much of their focus on the study of micro-pressure exit waves and subsequently their attenuation too. An entry compression wave is the very first of the oncoming successive waves formed as soon as the train enters the tunnel entrance plane. This preliminary wave is generated as the nose of the train approaches the tunnel entrance plane. The stationary air inside the tunnel gets compressed creating a piston effect. The generated wave reflects and hits back and forth creating a system of complicated waves. Only a small part of this generated wave exits the tunnel as a weak impulse wave (i.e. Micro-pressure wave). A drastic pressure drop also occurs as the train enters the tunnel"