Tunnel boom

The tunnel bang (English tunnel boom) is an aerodynamic phenomenon that occurs as a railway tunnel at high speed traffic ( HGV).

Origin and influences

At high speeds trains driving pressure waves speed of sound in front of it, on the share ever in the history of the tunnel in the back of the shaft, a higher pressure and thus a slightly higher temperature and a somewhat greater speed than in the anterior part arises. The pressure gradient is becoming larger and steeper. With the transition from the restricted section of the tunnel in unrestricted cross-section in the open, the pressure waves suddenly discharged by a bang.

The probability of the occurrence of the tunnel pop is increased by pulling speeds over 250 km / h unfavorable Zuggestaltung, tunnel cross sections below 60 m², tunnel length 5,000 m, low friction surface on the inner shell and the use of slab track.

As countermeasures, various measures have been developed: openings at the tunnel portal for pressure equalization, enclosures at the portal ( hood structures), trumpet-shaped cross-section expansions, increasing the sound absorption ability through structured surfaces, aerodynamic bow shapes of trains as well as decreased retraction speeds.

History

The tunnel bang was first observed in 1975 in Japan. On the local Shinkansen high-speed lines small cross-sections are common. As a countermeasure portal hoods have been developed. In Germany the phenomenon in 2005 made ​​her first appearance at ICE test drives through the tunnel Irlahüll and Euerwang.