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• Obtained the mechanism of pressure wave variation under different geothermal distributions. • Studied and summarized the influence of different geothermal distributions on the pressure wave peak. • Obtained the variation law of the dynamic temperature field in the tunnel. In this paper, experiments and numerical simulations are used to study the pressure wave transient laws, propagation characteristics and dynamic temperature field changes in tunnels located near geothermal hot springs. To simulate different temperature distributions, areas of 0–80 m, 80–160 m, 160–240 m and 270–350 m are heated, and the tunnel pressure wave peak value and train surface pressure wave peak value are studied accordingly. The research shows that when the heating zone is 0–80 m, the influence on the initial pressure wave is the greatest, the change rate is 8–10 %, and the initial expansion wave change rate is 5–10 %. When the heating zone is 80–160 m, there is little change in the pressure wave peak value in the first and second stages, and the expansion wave peak value is larger than the normal temperature in the third stage. When the heating zone is 160–240 m, the change rate of the pressure wave peak is small. When the heating zone is 270–350 m, there is a negligible change in the initial compression wave and expansion wave peaks in the first and second stages, and the change rate in the third stage is 2–4 %. Moreover, the heating zone located in front of the tunnel has a greater impact on the pressure at the tip of the train's nose, and the heating zones located in the middle and end of the tunnel have little effect on the initial positive peak value of the train pressure wave but a greater effect on the negative peak value. This study explores the influence mechanism of different geothermal distributions on pressure waves, which can provide more accurate boundary data for improving passenger comfort and the train thermal structural performance in high-temperature tunnels. [ABSTRACT FROM AUTHOR]

When a high-speed train (HST) passes the snowy ballast bed in winter, the slipstream can induce snow drifting and generate snow accumulation problem in the bogie region. The conventional numerical method has utilized the way that snow particles drift with the incoming flow around a stationary train with moving ground (STMG). In this paper, the sliding mesh technique is applied to reproduce the actual scene of a moving train with stationary ground (MTSG). Coupled with the discrete phase model, a novel simulation method for snow accumulation is presented. The comparisons between the STMG and MTSG are conducted, including the flow field, snow distribution and accumulation features. The results show that similar flow field around the HST is captured by the two methods. The MTSG predicts more dispersed snow distribution in the Bogie 2 region than the STMG. The total mass of accumulated snow on bogies and cavities obtained by MTSG is 18.31% more than that derived from STMG. The presented method achieves the relative motion among the HST-snow-ground and the sweeping process of the slipstream on the snow surface is fully considered. In engineering applications, it provides a feasible method to explore the snow accumulation phenomenon of HSTs in more scenes, such as the intersecting of two HSTs. • A novel snow accumulation simulation method for high-speed trains is presented. • The presented method achieved the relative motion among the train-snow-ground. • The slipstream-induced sweeping process on snow surface is considered. • The comparisons between the conventional and presented methods were conducted. • The mass was predicted 18.31% more by the presented method than the conventional. [ABSTRACT FROM AUTHOR]

• 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]

In this study, tests and simulations are used to investigate the changes in micro-pressure waves (MPWs) generated by high-speed trains passing through high geo-temperature tunnels. First, moving model tests of high-speed trains passing through local high-temperature tunnels are conducted, and then the simulation results are compared with the experimental results to verify the accuracy of the numerical algorithm. The results show that high temperature reduce the pressure gradient and alleviate MPWs. When the length of the high-temperature zone in the tunnel is within the streamlined length of the train (12.5 m), MPWs decrease as this length increases. When the length exceeds the streamlined length, MPWs basically no longer change. When the length equals the streamlined length and the air temperature in the tunnel reaches approximately 323 K, MPWs are reduced by 9.1%. This paper also presents the influence of the circumferential angle of the tunnel high-temperature zone on MPWs. MPWs gradually decrease with increasing heating angle when the angle is less than 225° and remain basically unchanged when the angle is greater than 225°. The results provide a method for mitigating MPWs and guidance for scholars who study MPWs mechanism in high geo-temperature tunnels. • Study the micro-pressure waves performance of trains passing through the high geo-temperature tunnels. • The characteristics of micro-pressure waves at different lengths L H in the high-temperature zone of the tunnel are analyzed. • The change law of micro-pressure waves under different circumferential angles i in the high-temperature zone are revealed. • Provide a method for mitigating noise pollution caused by micro-pressure waves of railway tunnels. [ABSTRACT FROM AUTHOR]

In this study, through experiments and numerical simulations, micro-pressure waves (MPWs) resulting from the movement of high-speed trains through high-temperature geothermal tunnels were studied, and a self-satisfying MPW mitigation method was proposed. First, a model experiment of a moving high-speed train under local high-temperature conditions was carried out. Then, a relationship between the MPW and length of the heating zone (L H) and the length of the train streamline (12.5 m) was established via numerical simulation. For L H < 12.5 m, the MPW amplitude gradually decreases with increasing L H. For L H > 12.5 m, the MPW amplitude remains basically unchanged. The influence of the circumferential distribution of the heating zone along the tunnel wall on the MPWs was further studied. The research results inspired an MPW mitigation method for tunnels, considering a heating length of 12.5 m and an angle of 225°. Moreover, in a tunnel, electric energy could be generated under slipstream action through a wind turbine installed to provide heating equipment with power, thereby achieving self-satisfaction. This research proposed a new MPW mitigation method for research on MPW mitigation. Moreover, new mitigation methods could facilitate the construction of an environmentally friendly society and provide a new approach to the sustainable development of cities. [Display omitted] • Obtained the influence of the length of the heating zone on MPW amplitude. • The relationship between the MPW and L H and the length of the train streamline was established. • Obtained the influence of the circumferential distribution of the heating zone on MPW. • A new self-satisfying MPW wave mitigation system is proposed. • A new MPW mitigation method and outlined new directions for research on MPW mitigation. [ABSTRACT FROM AUTHOR]