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Moving model simulations have been a key method of predicting the aerodynamic performances of High-Speed Trains (HSTs). Ideally, the aerodynamic characteristics of a train moving or being blown by the wind are the same with appropriate ground configurations. In a numerical simulation, there are differences due to interpolation errors and errors caused by model movement. The impact of the error caused by the movement on the result is not known. Therefore, in this study, stationary and moving cases were used to assess the magnitude of the movement's effect using the Improved Detached Eddy Simulation (IDDES) method. A wind tunnel test validated the numerical algorithm at 60 m/s and a common yaw angle of 0°. Moreover, the spatial and time discretization satisfied the high accuracy requirements, as determined through a mesh independence study and convective Courant number testing. The time-averaged drag coefficients predicted by the moving case were similar to those of the stationary case, especially the total drag coefficients. In contrast, differences were determined in the stationary and moving cases in terms of the flow structure and slipstream. The motion encouraged the streamwise vortices around the tail car and the wake vortices to expand along the spanwise direction and the wall-normal direction, and the vortex cores shifted away from the outer surface of the vehicle. As a consequence, the average value and the standard deviation of the slipstream increased. Therefore, moving model simulations require more caution. These findings can help researchers make directional corrections in the numerical simulation of train-tunnel systems. [ABSTRACT FROM AUTHOR]

Double unit trains running at high speeds may create additional aerodynamic challenges due to two streamlined structures with close proximity, exploring the aerodynamic performance of double unit trains is now critical. In this study, detached eddy simulation (DES) approach was employed to study the aerodynamic performance and the nearby flow patterns of a double unit train, whose results were compared and analyzed with that of a single-unit train with a same length. The results showed that the coupling method could change the aerodynamic drag on each car and tended to increase the overall drag of the double unit train. The lift force of the front car near the coupler was significantly increased. Similar slipstream distributions were found around the front half single and double-unit train except in a region close to the coupler. Due to the coupling structure, the slipstream of the rear half of double unit train was much stronger compared to single unit train. The vortex region behind the double-unit train was much wider than that of the single-unit train and was accompanied by greater vortex-shedding. [ABSTRACT FROM AUTHOR]

In this study, the aerodynamic performance of two trains that intersect inside a tunnel under ambient wind conditions is investigated. A full-scale test is conducted to verify the computational method and mesh, and then a series of numerical simulations are performed to investigate the pressure variation and the aerodynamic force coefficient by comparing with the condition of no ambient air. The difference between the results with/without ambient wind in a tunnel is analysed. The results indicate that if Train A travels downwind, the positive pressure of train surface increases and the negative pressure decreases as the wind velocity increases, and the arrival time of the maximum positive pressure lags on average 0.024 s and 0.058 s for wind velocities of 20 m/s and 40 m/s, respectively. For the tunnel wall measuring points, the maximum positive pressure increases as the wind velocity increases. The maximum drag coefficient of downwind Train A decreases by 4.7% and 10.1% for wind velocities of 20 m/s and 40 m/s, respectively, whereas that of upwind Train B increases by 5.7% and 15.8%, respectively. The maximum positive side force coefficient of downwind Train A increases by 20.8% for an ambient wind velocity of 40 m/s, whereas the same coefficient decreases by 16.7% for upwind Train B. [ABSTRACT FROM AUTHOR]

This study examined the slipstreams induced by high-speed trains (HSTs) passing through a tunnel using the improved delayed detached eddy simulation (IDDES) method. First, the flow fields in the open air and in a tunnel were compared. Furthermore, the flow in a tunnel was analyzed in detail, considering the development of both instantaneous flow structures and slipstream profiles at various measurement points. Finally, by considering four different nose lengths (4 m, 7 m, 9 m, and 12 m), the differences in the slipstream profiles and the wake flow induced by HSTs passing through a tunnel were determined. The results show that the piston effect had a significant influence on the slipstream profiles, causing a larger positive peak when a train passed through a tunnel. The peaks of the slipstream profiles decrease as the distances from the center of the track (COT) and the top of the rail (TOR) increases. The results show that a long nose length can reduce the scale and strength of the instantaneous x -vorticity and y -vorticity in the wake propagation region, thereby lowering the maximum slipstream peaks. The 12-m nose length train induced 56.7% lower velocity than the 4-m nose length train at y = 2 m beside the COT and z = 0.2 m above the TOR. In particular, the standard deviations of the positive peaks of the seven cross-sections decrease by 38.4% with the increase in the nose length from 4 m to 12 m, which means that a longer nose length can reduce the turbulence level in the wake propagation region. Consequently, from the perspectives of the safety and comfort of trackside people, a long nose length train is strongly recommended. [ABSTRACT FROM AUTHOR]