Maglev tunnel hoods can prevent speed-driven sonic booms

Currently, the world’s fastest commercial maglev train is China’s Shanghai Transrapid, which travels at 430 kilometers per hour. To go even faster, next generation maglev trains must contend with a loud problem: sonic booms. When a maglev train moving 600 km/h enters a tunnel, it produces micro-pressure waves that emit audible sonic booms, posing a threat to nearby humans, animals, and structures.

Wang et al. proposed a tunnel hood made of a foam metal material to mitigate the sonic booms generated by high-speed maglev trains. They developed a numerical simulation and validated it with data from miniature moving-model experiments to investigate how these porous media hoods affect micro-pressure waves, flow field evolution, and aerodynamic loads on the train when installed at tunnel entrances and exits.

They found the porous media hoods dampen the initial wavefront gradient at the entrance and reduce the intensity of the micro-pressure waves by enhancing radiation at the exit, effectively mitigating sonic booms. The hoods also decrease the magnitude and change rate of the train aerodynamic loads, which could improve the auditory experience of passengers and dampen train sway.

“This work can be used to guide the design of maglev tunnel hoods, thereby enhancing passenger comfort, improving vehicle dynamics, and reducing noise levels around tunnel portals,” said author Xiao-Hui Xiong.

Next, the authors will install porous media coatings on tunnel walls and investigate how they affect train-tunnel coupled aerodynamic effects.

“However, before applying foam metal hoods to high-speed maglev tunnels, it is necessary to verify their structural strength, service life, and other essential factors,” Xiong said. “Additionally, further advancements in foam metal materials are required to meet our desired performance specifications.”

Source: “Mitigation mechanism of porous media hood for the sonic boom emitted from maglev tunnel portals,” by Kai-Wen Wang, Guang Chen, Chih-Yung Wen, Xiao-Hui Xiong, Xi-Feng Liang, and Lei Zhang, Physics of Fluids (2024). The article can be accessed at https://doi.org/10.1063/5.0231438 .

This paper is part of the Flow and Civil Structures collection, learn more here .