Prediction of micro-pressure wave emissions from high-speed railway tunnels

With increasing train speeds micro-pressure wave emissions from tunnel portals can play a significant role in the assessment of the potential acoustic nuisance of a railway line. On the infrastructural side, appropriate counter-measures can be applied to the tunnel portals or to the tunnel interior to limit the emissions to accepted values. Therefore, an accurate prediction is needed to obtain the effectiveness of the counter-measures. This paper presents the tools currently in use by Deutsche Bahn AG to predict the three stages of the micro-pressure wave phenomenon by using full pressure signals in the time domain. The stages are examined independently with the pressure signal as interface parameter. The studies are started with three-dimensional CFD-simulations of the train entry into the tunnel portal to compute the entry pressure wave. In the next step the steepening of the wave inside the tunnel is modeled with a one-dimensional simulation tool considering steady and unsteady friction terms. Then the emission of the micro-pressure wave at the opposing portal with a far-field approximation of a vibrating circular piston solution is computed. All tools are validated by comparison with model-scale or full-scale measurements. The calculated pressure signals in the time domain are in good agreement with measured values. Finally, with knowledge of the complete pressure signal, the micro-pressure wave can be assessed acoustically as it is currently in discussion in Germany.