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With global warming intensifying, weather patterns become more volatile and extremes more common. Tornadoes are the most destructive natural disasters causing significant damage to infrastructure. Meanwhile, high-speed railways now face greater risks from tornado events as the national railway network and mass transit trains expand. Thus, studying the tornado flow characteristics and associated effects on high-speed trains is necessary. A study is presented regarding the wind-loading characteristics of a high-speed train running over a railway bridge induced by a tornado belonging to the future railway network. The wind-loading characteristics analyses are performed using the improved delayed detached eddy simulation method. After verifying the numerical approach and mesh strategy, computational studies are conducted to produce a tornado-like vortex and investigate the tornado-induced wind-loading characteristics of a high-speed train running on the bridge by combining a tornado simulation with a moving mesh technique. For the wind-loading parameters studied herein, the selected train's velocity range is between 50 and 350 km/h, the typical operation speed of either regular or high-speed trains. The numerical results show that the time histories of aerodynamic forces on the train revealed a pattern in tornadic flow variability, the time evolutions of the wind loads on the train were affected by train speeds, and the fluctuation was the greatest when the train ran at 50 km/h. Moreover, the train is subjected to larger aerodynamic forces and moments when it operates along with the rotating vortex flow, especially in the core region, and the train is more dangerous when it runs at a lower speed. The results in this study provide references for assessing operation safety, while a train running on the bridge encounters tornadoes. [ABSTRACT FROM AUTHOR]

To better understand the aerodynamic characteristics of a train-bridge system under crosswind, an in-house experimental apparatus was developed in a wind tunnel at Central South University (CSU). The new facility consists of trains, a bridge, U-shaped slide rails, and positioning systems with winches. A wireless data acquisition system for pressure measurements was mounted within the train carriage to avoid any potential aerodynamic interference. A 1:25 scaled model of CRH2 running over a simply supported girder bridge was tested in a wind tunnel. The aerodynamic characteristics of the train-bridge system under various combinations of crosswind speed, train speed, and vehicle location on the bridge were identified. The experimental results reveal that the cosine law for surface wind pressure on a train under crosswind is no longer valid when the train runs on the bridge. The moving model method can better capture the more practical aerodynamic characteristics and the impact of train movement on the bridge. The present study indicates that the wind tunnel experiments using the stationary model cannot fully reveal the aerodynamic characteristics of both the train and bridge during crossing. The results captured using this unique approach provide insight into the aerodynamic characteristics of trains and bridges. [ABSTRACT FROM AUTHOR]

• Aerodynamic characteristics of a typical high-speed railway viaduct under tornado near-ground winds were studied. • Surface pressure coefficients of the bridge deck vary from place to place within the tornado. • Largest side and lift forces occur at the tornado core, but the change patterns of forces in different types with the variation distance. • Research findings are helpful for the design, operation & maintenance of high-speed railway bridges. The tornado is in direct contact with the underlying surface, which causes damage and indicates the vortex structure close to the ground. Accordingly, the maximum wind velocity generally could occur near the ground, potentially exposing the infrastructure to higher wind loads. However, one of the biggest challenges facing tornado research is characterizing the wind structure very near the surface due to the limitation of the data by using Doppler weather Radar. Considering the advantage of the high-fidelity computational fluid dynamics (CFD) models, this study aims to investigate the aerodynamic characteristics of a high-speed railway viaduct under tornado near-surface winds. More specifically, in light of limited full-scale data to arrive at a consensus on quantifying key parameters characterizing the tornado flow and near-surface winds, firstly. Secondly, tornado radar-measured data and a theoretical analysis model were utilized to validate the accuracy of the numerical method adopted in this study. Thirdly, the wind pressure distribution on the bridge is validated using the wind tunnel experimental data in Central South University(CSU), and the comparison between the simulational bridge and the measured data under crosswind was satisfactory. Finally, a comprehensive modeling strategy comprehensively investigates the aerodynamic characteristics of a high-speed railway viaduct under a tornado near-surface wind. [ABSTRACT FROM AUTHOR]