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• Study the mitigation effect of pressure fluctuations caused by train intersection in a tunnel with the enlarged end. • Consider the effects of the total length of tunnels and unit number of trains on the optimal length of the enlarged section. • Analyse the mitigation principle of the pressure fluctuations impacted upon trains. • Obtain an optimal length coefficient to attain the maximum mitigation of the pressure fluctuations. Intense pressure fluctuations generated by the intersection of high-speed trains (HSTs) in a tunnel are unfavourable for the comfort of passengers and the safety of HSTs and tunnel facilities. This study numerically investigated the mitigation principle of the pressure fluctuation impacted upon HSTs using the enlarged tunnel end with taking into account the total tunnel length and the unit number of HSTs. Moving model tests were also performed to validate the numerical method based on the unsteady RANS equations and RNG k - ε turbulence model. The numerical results show that the enlarged end of a tunnel can manifestly alleviate the negative pressure induced by the train intersection and the length ratio of the optimal length of the enlarged section to the total length is in the range of 0.26–0.28. The optimal length of the enlarged section can be implemented by synchronising the contact of the derived waves with the train intersection. Moreover, the increase in the marshalling number of HST augments the mitigation effect of the enlarged section. This study gives insight into the mitigation of the pressure fluctuation in tunnels and can provide valuable data and a theoretical basis for the tunnel design when considering the aerodynamic effect of HST intersection. [ABSTRACT FROM AUTHOR]

• Obtained the influence of the length of the heating zone on the peak value of the initial compression wave. • Obtained the influence of the length of the heating zone on the peak value of the initial expansion wave. • Study the effect of different heating zone lengths on the peak value of the train's initial compression wave. • The result of the initial temperature field of the tunnel is obtained. • Study the dynamic change process of temperature during train operation. In this paper, through experimental and numerical simulation methods, the influence of the tunnel heating zone length on the pressure wave peak and temperature field changes is investigated in tunnels with different heating zone lengths. The accuracy of the applied simulation algorithm is verified against experimental data from moving model tests. Via numerical simulations, the changes in the pressure wave peak value and temperature field are explored with five heating zone lengths. For the compression wave, this research revealed that when L H (length of the heating zone) < L T (length of the train) and that with an increase in L H , the peak value of the initial compression wave notably decreases. When L H > L T , the compression wave peak value remains basically stable. In regard to the expansion wave at tunnel measurement points, for L (from tunnel entrance) ⩽ 110 m, the initial expansion wave peak exhibits small fluctuations. At L > 110 m, with an increase in the heating zone length, the peak value of the expansion wave peak gradually decreases. In addition, the dynamic temperature field changes. The obtained research results provide a new idea to reduce the peak pressure value in a tunnel. In addition, this study provides a method for pressure wave mitigation during tunnel design and guidance for passenger comfort improvement in future city railway tunnels. [ABSTRACT FROM AUTHOR]

A moving model (1/20 scale) was used to study the effect of high temperature at the entrance of a tunnel on the aerodynamic performance of a high-speed train passing through it. The air in the tunnel was heated using highly-precise, self-controlling, ultra-thin, silicone rubber heating devices that were firmly attached to the inner surface of the tunnel (covering the first 2 ​m of the tunnel from the entrance). When the specified temperature was reached, tests were performed using a model train moving at different speeds. The experimental results were used to compare and analyze the pressure fluctuations and propagation of pressure waves under normal and localized high-temperature conditions. The results show that the peak-to-peak value of the transient pressure on the tunnel surface decreases by 5–7% in the presence of a normal ambient and high temperature tunnel mode. In addition, the corresponding difference on the surface of the head of the train is 3–4%. Hoping this experimental study will encourage theoreticians to investigate the mechanism responsible for the generation of transient pressures in localized high temperature railway tunnels. The results can provide guidance and support for researchers seeking to improve passenger safety and comfort in high temperature railways. • Study the influence of the local high temperature difference by a moving model test. • Obtain the aerodynamic performance of trains passing through the tunnel under heat. • Compare the pressure curve difference between normal temperature and heating. • Analyze the difference of the pressure change and pressure propagation characteristic. • Study the pressure peak-to-peak difference under normal and heating. [ABSTRACT FROM AUTHOR]

Alleviation of the pressure transients caused by high-speed trains intersecting in a tunnel with partially reduced cross-section is investigated by numerical simulation. The RNG k - ε turbulence model and hybrid grid are adopted for the numerical simulation, which is validated by the moving model test. Two factors, the length of reduced section (L) and the train marshalling number, are considered to analyse the alleviation effect. The results show that, for reduction of the pressure transients induced by the intersection of three-car marshalling trains, the location of the change in cross-section is supposed to be near the location of the maximum value of the initial expansion wave (L → 240 ​m). In addition, for four-car marshalling trains intersecting in a tunnel of L ​= ​240 ​m, the excavation volume of the tunnel (tunnel volume) decreases by 14.4%, and the average pressure amplitude on the train surface decreases by 7.9%. Especially the pressure amplitude at the measurement point in the streamlined area of the tail car decreased by 28.6%. The reduced section tunnel has a good effect on decreasing the pressure transients around train body and the tunnel excavation volume (construction cost), which helps the tunnel design process. • The influence of the reduced section on the pressure transients in high-speed train tunnels are analysed. • For high-speed trains intersecting in the tunnel, the optimal location of the change in cross-section are obtained. • The excavation volume of the tunnel and the average train surface pressure amplitude decreases by 14.4% and 7.9%. [ABSTRACT FROM AUTHOR]

• History of aural sensations was visualized during the train's running in tunnels. • Effect of speed, seal index, car No. and tunnel length on ear comfort was revealed. • Ear sensations were classified into four levels based on the duration of discomfort. • Mathematic model was established to predict pressure-related ear comfort in trains. • A way to seek for preferable speeds was put forward for given train and rail lines. Aural comfort is negatively affected during a train's passage through various tunnel environments. The objective of this study was to propose a prediction model for determining optimal operation parameter combinations to improve train occupants' aural comfort. High-speed train model tests, combined with a mathematical transfer model, were used to obtain the interior pressure transients under varying speeds, tunnel lengths and seal indexes. Then, a middle ear finite element model was used to simulate the dynamic responses under the pressure transients, and three indicators were employed to assess the severity of aural sensations. Meanwhile, the aural discomfort were classified into four groups according to the duration. Based on the simulation results, the ordinal regression analysis method was used to reveal the effects of the considered factors on aural comfort. The results indicate that aural discomfort sensations begin when a train runs in the middle of a tunnel but are mitigated when it approaches the tunnel exit. Furthermore, aural discomfort is positively correlated with the train speed and the distance from the driver cabin of the head car but negatively correlated with the seal index and tunnel length. As a conclusion, a mathematical prediction model was established that incorporates factors including the train speed, seal index, tunnel length and car position. It can not only forecast aural sensations under certain operation parameters and tunnel environments but also be used for determining the optimal operation parameters to ensure the best aural sensations for high-speed-train occupants. [ABSTRACT FROM AUTHOR]