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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]