Experimental Study of the Compression-Wave Generation due to Train-Tunnel Entry
The entry of a high-speed train into a tunnel leads to a complicated system of pressure waves inside the tunnel. The change in pressure can have negative effects on the structures of the train and of the tunnel as well as on the passenger comfort. In longer tunnels, the propagating wave fronts can steepen and a disturbing micro pressure wave - also known as tunnel boom - can be radiated from the opposite end of the tunnel. All these problems related with the pressure waves may become even more severe during the next years, because many recently-built tunnels are twin-bore tunnels with a single track in each tube. Hence, the cross-sectional area of a tube is smaller than the one of a conventional double-track tube, which goes along with stronger pressure waves.
The crucial parameter for the negative effects is not the height of the generated pressure waves alone. More important is the pressure gradient or temporal derivative of the pressure in the wave fronts. Extended tunnel portals equipped with opening vents can be used to reduce these gradients. For example, such portals can be found at the recently-built Katzenberg tunnel in the south of Germany.
To investigate the characteristics of the generated pressure waves and the influence of an extended tunnel portal, a new facility was built at the German Aerospace Center DLR in Göttingen, the so-called “Tunnel-Simulations-Anlage” (TSG). This facility is basically a moving model rig, where the model train moves along the rail through air at rest and enters a fixed model tunnel. The facility has a length of 60 m and can be equipped with model tunnels of more than 10 m in length. Figure 1 shows a model tunnel with extended portal.In the present case, the tunnel has a length of 10 m and the extended portal consists of a hood with a length of 1.67 m. The train is a model of the German high-speed train ICE3 with the scale of 1:25. The tunnel hood has twelve opening vents on each side also called windows in the following.
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 more than 100g. The catapult is designed to reach a maximum speed of 100m/s.
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. This was tested using two different extended portals, a completely vented and an unvented one. The results of the two portal configurations compared to the results of the clear configuration without hood are depicted in fig. 2. The curves were measured s=4.35m behind the tunnel entrance with a model velocity of U=44m/s.
It is evident that a significant decrease of the maximum pressure gradient can be achieved by using a tunnel hood. Nevertheless, there is only a small difference between the vented and the unvented hood, which leads to the conclusion that by adjusting the number of the vents the portal effectiveness can be further improved.
To verify this, additional tests were performed with partially closed openings. In one case 1/3 of the windows were closed and in a second case 2/3. Figure 3 shows the temporal evolution of the pressure gradient for these cases in comparison to the completely vented and the unvented case, which were already presented above. Indeed the portal performance can be improved by closing some of the windows. Further tests showed that with the relative small opening area of one single window on each side a reduction of the pressure gradient can be achieved even below the values achieved in the 1/3 or 2/3 case. It turned out that the position of the single opening has a strong influence of its effectiveness.
D. Heine & K. Ehrenfried: Experimental Study of the Pressure Rise due to Tunnel Entry of a High-Speed Train, Notes on Numerical Fluid Mechanics and Mulitdisciplinary Design, Vol. 124, p. 335-342, 2014
Dr. rer. nat. Daniela Heine
German Aerospace Center (DLR)
Institute of Aerodynamics and Flow Technology, Department Ground Vehicles
Phone: +49 551 709-2297