Trains of the Future Is France's Energy-Guzzling TGV Prototype the Right Answer?
Part 2: The Perils of High-Speed Train Design
That figure is the benchmark, in any case, for a research project that Sigfried Loose, a Göttingen-based DLR aerodynamics expert, is working on together with Canadian train manufacturer Bombardier. The project is called "Next Generation Train" and it is meant to set the stage for the train of the future. That train will be "faster, lighter, safer and at the same time quieter," pledges DLR chairman Johann-Dietrich Wörner. Of course, he knows well that the goals he is announcing tend to be mutually exclusive in physics.
Loose's main goal consists in eliminating so-called "show stoppers" -- serious problems whose solution is an absolute precondition for further speed increases. The greatest problem is the danger of crosswinds, he says.
At the very latest, the recent gale-force winds of the storm " Kyrill" that forced Deutsche Bahn to suspend train travel in some regions, showed German people that one of the major factors of fear of flying also applies to train travel. Up until now, the only cases of trains being blown off the tracks have happened with lighter commuter trains. Narrow-gauge trains have even been known to topple over while standing still, but usually without causing any serious harm to people.
A complete ICE train weighs more than 800 tons. It's not likely to be knocked over by wind blasts -- at least not while standing still. But things change when a train is traveling at 350 kilometers per hour. At those speeds, the head of the train is exposed to considerably less gravitational pull and could actually topple if hit by an abrupt crosswind. Aerodynamics experts have already calculated this effect in models: It could lead to a train disaster of a similar magnitude to the 1998 ICE crash in Eschede, Germany that killed 101 and injured 105.
A number of safety precautions are in place to prevent such a disaster from happening. High-speed train tracks are lined with wind-protection fences in especially critical areas. And SNCF has set up a warning system along the southern Marseille-bound route, where strong mistral winds lurk, so that such strong winds can be noticed in time and train speeds reduced if necessary.
In addition, safety authorities like Germany's Federal Train Agency require train manufacturers to prove that their trains are resistant to crosswinds of a pre-defined force when traveling at maximum speed. Resistance to crosswinds moving at 28.8 meters (94.5 feet) per second -- the equivalent of wind force 11 on the Beaufort scale -- is considered the standard.
Modern high-speed trainsets "are already reaching their limits in this regard," says Alexander Orellano, the leading aerodynamics expert at train manufacturer Bombardier. In the trainsets for the most recent ICE models in Germany, the engine is distributed underfloor along the length of the train and there are no separate locomotives at the train ends. This makes the head of the train even more sensitive to gusts.
But the advantages the motorized trainsets bring with them -- better traction and considerably higher passenger capacity -- are pushing all major train manufacturers to develop them. Even Alstom -- a company that swore by conservative and robust locomotive trains up until now will soon present its first motorized train sets in the form of TGV's successor, the AGV. But no information has been unveiled yet about the new train's aerodynamic characteristics or wheel load.
Designing the train of tomorrow
ICE manufacturers still resort to the solution of applying steel plates to the ends of the train in order to make them heavier. It's a simple solution -- and one that contradicts DLR's goal of reducing overall train weight. Loose envisions a train that is 30 percent lighter than today's trains while still resting stably on the tracks.
Model trains the size of those produced for train fans by German toy company Märklin and DLR's wind tunnels are the tools he uses in his research. The model trains are sometimes specially produced by him and sometimes purchased in toy shops and subsequently re-worked until they have the shape needed. The wind tunnels are among the best facilities in the world and use extreme refrigeration and compression to make air so dense that even model tests yield realistic results.
The physicist wants to present a first train model towards the end of the year. It will probably be equipped with spoilers not unlike those found on the front of race cars. As far as the basic shape of the head of the train is concerned, a number of very different variants are being discussed. Loose needs to bear in mind an additional phenomenon that train producers largely disregarded until now: the sonic boom in tunnels.
Trains thrust into tunnels like the piston of a bicycle pump, creating a pressure wave that races ahead of the vehicle at the speed of sound. This can lead to a thunderlike sound at the end of the tunnel, similar to that caused by planes traveling faster than the speed of sound. In Japan, where homes are often built close to train tracks, this phenomenon has caused windows to shatter.
Furthermore, part of the pressure wave returns into the tunnel with negative pressure and then races past the passengers in the approaching train. The acoustic effect, similar to that of a slap in the face, becomes all the more painful the faster the train's speed and the narrower the tunnel.
But tunnels are becoming narrower: For security reasons, only single passageway tunnels are being dug out, and the cross section has decreased from 90 square meters to 60. As Loose says: "That will be unbearable for passengers traveling in today's trains even at a speed of 300 kilometers an hour."
- Part 1: Is France's Energy-Guzzling TGV Prototype the Right Answer?
- Part 2: The Perils of High-Speed Train Design