Formation and propagation characteristics of a weak shock wave in maglev tube

Pressure changes outside a train can be transmitted into a carriage when the train is running in the tunnel, seriously affecting passenger comfort. In this paper, the polynomial response surface (PRS) is used to predict the value of the compression wave and obtain the predictive model equations. For the traveling pressure waves, many influencing factors contribute differently to the final pressure wave form and magnitude. In geothermal tunnels, the speed of a high-speed train (V), air temperature of the inner tunnel (T), and atmospheric pressure (P) are the three main influencing parameters. Using a PRS prediction model, the sensitivity of each influencing parameter is analyzed by the Sobol sensitivity method. The result shows that V has the greatest effect on the pressure peak value, and T has the least effect. The initial compressional waves and expansion waves are most and least sensitive to T, respectively. The coupling effect among parameters P, T, and V is relatively small. Using the sensitivity results of the parameters, targeted and reasonable parameter adjustment can effectively relieve the pressure inside and outside the train and improve passenger comfort in geothermal tunnels. These results provide important technical support for the mitigation of pressure waves.

Prediction and sensitivity analysis of the pressure wave peak value induced by the high-speed train in the long tunnel under a high geothermal environment

Wang,

Wang

et al. 2024

Mitigation mechanism of porous media hood for the sonic boom emitted from maglev tunnel portals

Wang,

Chen,

Wen

et al. 2024

The micro-pressure waves (MPW) released from maglev tunnel portals can generate audible sonic booms and cause structural resonance in surrounding buildings, posing challenges to developing high-speed maglev trains. This paper proposes a novel porous media hood (PMH) and investigates its mechanism for mitigating the sonic booms emitted from tunnels. The numerical model employs the improved delayed detached eddy simulation turbulence model and overset grid technology, validated against data from moving-model experiments. The influences of the PMH's inherent properties and geometric parameters on MPW, flow field evolution, and aerodynamic loads on the train body were comprehensively discussed. The research demonstrates that PMH effectively dampens the initial wavefront gradient at the entrance and reduces the MPW amplitude by intensifying radiation within its exit vicinity. The porosity of 0.2 facilitates a seamless transition for the streamlined head from the ventilated PMH to the airtight tunnel. Lengthening the PMH enhances its MPW mitigation effect, whereas the impact of PMH thickness is minor. The PMH effectively diminishes the reflection intensity of compression and expansion waves at the tunnel ends, leading to a reduction in the magnitude and changing rate of train aerodynamic loads. This underscores the PMH's potential to enhance passengers' auditory comfort and alleviate issues related to train sway.

Characterizing a device for easy simulation of compression waves induced by trains passing through tunnels

Liu,

Wei,

Yang

et al. 2024

When a high-speed train enters a tunnel, an initial compression wave (ICW) is generated, which radiates out as it propagates lengthways through the tunnel to the exit, forming an uncomfortable micro-pressure wave (MPW). The aim of this research is to develop a scaled device to quickly simulate this aerodynamic phenomenon. Our device achieves this by using the instantaneous release of high-pressure air in the chamber. In the first part of the paper, the reliability of this device is verified by various methods, including an airtightness check, calibration of transducers, and repeatability experiments. Next, the mapping of the parameters of the device to engineering values is discussed. The propagation process of the ICW and the pressure fluctuations in the tunnel are then analyzed, and the discussion centers around a control variable case. Finally, the MPW generated near the tunnel exit is explored and acoustically evaluated. It is found that the initial pressure in the chamber, the opening voltage, and the number of solenoid valves in the experiment can be mapped to the train speed, the characteristic length of train nose, and the blockage ratio, respectively. When the pressure amplitude of the ICW is higher, there will be a certain steepening phenomenon in the propagation process. The pressure fluctuation cycle in the tunnel is calculated as 4× tunnel length/wave velocity, and the amplitude of fluctuation decays exponentially over the cycles. In most cases, the sound pressure level of MPWs near the tunnel exit exceeds the hearing threshold, based on the auditory properties of the human ear.