Computational analysis and mitigation of micro-pressure waves in high-speed train tunnels

Abstract

Tunnels are increasingly used in high-speed rail projects to mitigate against issues such as environmental noise, land disputes, and unsuitable terrain. However, the trend for increasing train speeds will result in unacceptable noise emissions from tunnels without the use of effective countermeasures. Novel countermeasures for the propagation of pressure waves in tunnels and the emission of sound waves into the environment, commonly referred to as micro-pressure waves, were numerically investigated in this work.

This following countermeasures were considered: (1) the design and optimisation of an array of Helmholtz resonators embedded in redundant tunnel space; (2) a preliminary parametric study on the effect of modifying the junction geometry between the tunnel and side branches (e.g. ventilation shafts) for noise emissions from side branches.

Helmholtz resonators are used extensively in engineering disciplines where noise attenuation is an important factor (e.g. jet-engine liners). However, their ability to suppress noise emissions from tunnels has not been demonstrated. This work investigates the effectiveness of these countermeasures when applied to a representative tunnel system and compares their performance to existing ones (e.g. tunnel entrance hoods) using numerical techniques.

One and two-dimensional models were developed to predict the performance of these countermeasures, subject to realistic geometric constraints and operating conditions. The geometry of the array is optimised to provide robust performance over a range of operating conditions. The numerical predictions are validated against experimental data, and are benchmarked against analytical predictions and CFD. Finally, the combination with existing countermeasures is studied and enhancements to the models are proposed. Both countermeasures were found to work effectively for a physically representative system.