Abstract: In this study, an improved delayed detached eddy simulation (IDDES) method based on the shear-stress transport (SST) k-ω turbulence model has been used to investigate the underbody flow characteristics of a high-speed train operating at lower temperatures with Reynolds number Re=1.85×10⁶. The accuracy of the numerical method has been validated by wind tunnel tests. The aerodynamic drag of the train, pressure distribution on the surface of the train, the flow around the vehicle, and the wake flow are compared for four temperature values: +15 °C, 0 °C, -15 °C, and -30 °C. It was found that lower operating temperatures significantly increased the aerodynamic drag force of the train. The drag overall at low temperatures increased by 5.3% (0 °C), 11.0% (-15 °C), and 17.4% (-30 °C), respectively, relative to the drag at +15 °C. In addition, the low temperature enhances the positive and negative pressures around and on the surface of the car body, raising the peak positive and negative pressure values in areas susceptible to impingement flow and to rapid changes in flow velocity. The range of train-induced winds around the car body is significantly reduced, the distribution area of vorticity moves backwards, and the airflow velocity in the bogie cavity is significantly increased. At the same time, the temperature causes a significant velocity reduction in the wake flow. It can be seen that the temperature reduction can seriously disturb the normal operation of the train while increasing the aerodynamic drag and energy consumption, and significantly interfering with the airflow characteristics around the car body.

Key words: High-speed train (HST); Low temperature; Aerodynamic characteristics; Cold region; Improved delayed detached eddy simulation (IDDES)

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