Keywords: Tunnel-Simulations-Anlage Göttingen, train aerodynamics, tunnel entrance, high-speed train, tunnel portal, pressure-wave propagation.

The entrance of a high-speed train into a tunnel leads to a complicated system of pressure waves inside the tunnel. The change in pressure can affect the structures of the train and of the tunnel, as well as the comfort of the passengers. This influence will become even more important during the next years, because many recently built tunnels are single track tunnels with two tubes, so the cross-sectional area of each tube decreases, which goes along with increasing pressure waves.

The main challenge of the engineers therefore is to reduce the influence of these pressure changes on the passengers, the tunnel and the train, which can be achieved by building a tunnel portal at the tunnel entrance being equipped with several windows. The influence of these portals has to be studied to optimize the shape and size of the windows and of the portal itself.

To investigate the characteristics of the generated pressure waves and the influence of an extended tunnel portal, a new facility was build at the German Aerospace Center DLR in Göttingen, the so-called "Tunnel-Simulations-Anlage" (TSG). This facility is basically a moving model rig, so the model train moves along the rail through the air and enters the fixed model tunnel. The facility has a length of 60m and can be equipped with a tunnel of 10m length.

The catapult to accelerate the train is based on the techniques of an ancient roman ballista and the catapult of an aircraft carrier. It is possible to achieve a maximum acceleration of about 100g, which can result in an aimed maximum speed of 100m/s. The model train is a model of the German high-speed train ICE3 with the scale of 1:25.

It will be shown that the compression-wave generation due to train-tunnel entry can be investigated with the help of the new facility.

The first experiments were made without an extended portal to examine the unaffected pressure waves. All the waves inside the tunnel are reflected at the end of the tunnel, so that a very complicated system of pressure waves occurs. Using an extended portal especially the first pressure rise can be flattened. Furthermore the observed propagation speed of the acoustic signals does not equal exactly the expected speed of sound due to the tunnel walls, which are not completely inelastic.

The influence of an extended portal will be considered, as well as frictional effects, and the experimental data are compared with numerical and analytical results.

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