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nvestigates ultra high-speed


The TSG is also being used to investigate the propagation of pressure waves in tunnels, another major challenge. The faster a train travels and the narrower the tunnel, the higher the pressure; in addition when pressure waves reach the tunnel portal they are partially reflected back into the tunnel which puts increased aerodynamic forces not only on the train but also on the tunnel structure - not to mention the acoustic shock for the passengers. This becomes even more pronounced when trains pass in double-track single-bore tunnels.


One of the two specially-designed tunnels to investigate various factors affecting train behaviour.


alone where this is likely to have been a factor. One of the most critical times is when a train comes out of a wind shadow - a tunnel for example - and is suddenly subject to a cross wind.” The same applies if a train is crossing a bridge or if there is an oncoming train. To measure this effect, the TSG is equipped with a 5m wind channel module as well as the plexiglass tunnel. Here the model can be subjected to cross winds directed at various angles,


IRJ July 2013


and the flow structures can be observed with the use of smoke and laser beams. The effect of cross winds can also be measured in the cross-wind tunnel (SWG), a closed system with a model train inside attached to a fixed plate. The flow field is obtained by means of particle image velocimetry (PIV), which gives a picture of the forces at work. In addition, aerodynamic loads are measured with a strain-gauge balance in the rear car.


One solution is to install vertical ventilation slots at the tunnel entrance so that the pressure builds up more slowly and smoothly. Small sensors placed in fixed positions along the plexiglass tunnel measure the pressure during a test, and the model train is equipped with a pressure sensor, an acceleration sensor and a light sensor. Data is recorded by computer to form the basis for calculations to find the optimum configuration. A German Rail (DB) ICE3 is almost completely airtight and has extra thick walls to counter the effect of these pressure waves. If the proposed double- deck train has even stronger seals it will be heavier and need more energy, which is why another solution has to be found. Part of the NGT project is to develop lightweight trains, with for example sandwich structures comprising a honeycomb core and glass-fibre reinforced skin. This coupled with energy saving techniques during acceleration and braking would reduce energy consumption considerably and help to cut emissions. Flying ballast is a growing problem. Formerly associated with the accumulation of ice and snow beneath a train, the phenomenon has now become more prevalent at other times of the year, since the aerodynamic forces generated by the current generation of ICE trains is enough to lift ballast off the track. Dillmann refers to an avalanche effect: one stone is spun into the underside of the train, dislodges two or three more as it falls, and so on. “This can do enormous damage to the underside of a train,” he says. To find a solution, PIV measurements from a water tank wagon on a model train are being collected to provide information


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