Aerodynamic effects of high-speed train pantographs passing through different typical tunnels

This study investigates abnormal oscillations of high-speed pantographs in tunnels using the Improved Delayed Detached Eddy Simulation (IDDES) method and overset grid technology, analyzing aerodynamic forces, flow patterns, and spectral characteristics under different train speeds and tunnel cross-sectional areas. The results show that the aerodynamic behaviour of the pantograph can be divided into three stages: open air, transition section and tunnel. In tunnels, the time-averaged value and fluctuation intensity of the aerodynamic force coefficient are higher than in open air, with the disparity increasing as train speed and tunnel blockage ratio rise. In the transition section, the train and pantograph entering the tunnel generate pressure waves, which lead to significant fluctuations in the aerodynamic force of the pantograph. The dominant frequency of the aerodynamic force varies depending on the train speed, tunnel cross-sectional area, and track type. Different from the dominant frequency of 134 Hz observed in the open air, the power spectral density of aerodynamic drag and lift in the tunnel presents multiple harmonic peaks. The fundamental frequency shows a positive correlation with both train speed and tunnel blockage ratio, increasing as train speed rises and tunnel cross-sectional area decreases. The coupling of complex vortices will increase the instability of the flow field, affect the dynamic response of the pantograph, and may induce oscillation.