Tunnel bang
The tunnel boom (engl. Tunnel boom ) is an aerodynamic phenomenon in high-speed traffic (HGV) when passing through railway tunnels occurs.
Origin and influences
At high speeds, trains propel pressure waves at the speed of sound in front of them, which continue to split up in the course of the tunnel: a higher pressure is created in the rear part of the wave and thus a slightly higher temperature and a slightly higher speed than in the front part. As a result, the pressure gradient becomes larger and steeper. With the transition from the restricted cross-section of the tunnel to the unrestricted cross-section outdoors, the pressure waves suddenly discharge with a bang.
The likelihood of a tunnel bang is increased by train speeds over 250 km / h, unfavorable train design, tunnel cross-sections under 60 m², tunnel lengths over 5,000 m, low friction surface on the inner shell and the use of the slab track .
In order to avoid a tunnel bang, various countermeasures have been developed: openings in the tunnel portal for pressure equalization , housings on the portal (hood structures), trumpet-shaped cross-sectional expansions, an increase in the sound-absorbing capacity through structured surfaces, aerodynamically optimized bow shapes of trains and reduced entry speeds. If a train accelerates after entering the tunnel, there is usually no tunnel bang.
history
The tunnel bang was first observed in Japan in 1975. Small cross-sections are common on the Shinkansen high-speed lines there. Portal hoods were developed as a countermeasure. In Germany, the phenomenon first appeared in 2005 during ICE test drives through the Irlahüll and Euerwang tunnels .
Web links
- By a nose's length: test for the fastest train in the world. heise online, April 19, 2006, accessed on July 23, 2010 .
Individual evidence
- ↑ a b c d G. Brux: Tunnel bang: emergence and countermeasures . In: Bautechnik , issue 10/2011, p. 731 f. doi: 10.1002 / bate.201101504 .