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Porous wind barriers (PWBs) are gradually applied to tunnel–bridge–tunnel infrastructures (TBTIs) along high-speed railway lines. Due to the remarkable aerodynamic effect of high-speed trains (HSTs), the windproof performance of a PWB at tunnel–bridge section (TBS) is particularly critical when a HST passes through the TBTI under crosswind. And it seems to be easily ignored by researchers. This study aims to determine the influence mechanism of the PWB in the TBS. A CFD dynamic model of air–train–PWB was built based on porous media theory, and its reliability is verified by model and field tests. The main results are as follows: the corresponding variation amplitudes of the train’s aerodynamic load coefficients are reduced by 36–95% when a PWB is set in the TBS; adopting the same design parameters along the full-length PWB on the TBTI is unreasonable; the PWB height and porosity in the TBS must be increased and reduced more than 33%, respectively, to achieve equivalent windproof performance. The conclusions in this paper can provide a preliminary idea for the optimization design of the PWB on the TBTI.

Porous wind barriers (PWBs) are gradually applied to tunnel–bridge–tunnel infrastructures (TBTIs) along high-speed railway lines. Due to the remarkable aerodynamic effect of high-speed trains (HSTs), the windproof performance of a PWB at tunnel–bridge section (TBS) is particularly critical when a HST passes through the TBTI under crosswind. And it seems to be easily ignored by researchers. This study aims to determine the influence mechanism of the PWB in the TBS. A CFD dynamic model of air–train–PWB was built based on porous media theory, and its reliability is verified by model and field tests. The main results are as follows: the corresponding variation amplitudes of the train's aerodynamic load coefficients are reduced by 36–95% when a PWB is set in the TBS; adopting the same design parameters along the full-length PWB on the TBTI is unreasonable; the PWB height and porosity in the TBS must be increased and reduced more than 33%, respectively, to achieve equivalent windproof performance. The conclusions in this paper can provide a preliminary idea for the optimization design of the PWB on the TBTI. [ABSTRACT FROM AUTHOR]

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Highlights • A 3D unsteady incompressible numerical method is adopted. • The transient characteristics of aerodynamic loads of the HST are analyzed. • The sudden change mechanisms of the aerodynamic loads are revealed from flow field. Abstract Windbreak (WB) and anti-wind open-cut tunnel (AOT) are two common windproof facilities for high-speed railways in windy areas. This study aims to determine which of them has better aerodynamic performance. For this purpose, the transient aerodynamic loads of high-speed trains are compared when passing through two windproof facilities under the same conditions of train and crosswind speeds via CFD simulation. The sudden change mechanism of aerodynamic loads and the differences in aerodynamic loads between the AOT and WB cases are revealed from the perspectives of flow field and pressure. Four main conclusions are obtained. Firstly, the fluctuation amplitudes of the five aerodynamic loads of each carriage in two periods (entry and exit) are remarkably greater than those in other periods (completely running in crosswind or windproof facilities). Secondly, the maximum fluctuation amplitudes of the five aerodynamic loads of the head carriage are generally greater than those of the rear and middle carriages during the period of entry (or exit). Thirdly, the maximum fluctuation amplitudes of side force, lift force, rolling moment, yawing moment and pitching moment of the head carriage in the WB case are 1.42, 0.84, 1.42, 1.45 and 1.44 times for the period of entry and 1.2, 1.24, 1.2, 1.58 and 2 times for the period of exit, respectively, compared with those in the AOT case. Fourthly, the maximum change rates at a time interval of 0.035 s of the side force, lift force, rolling moment, yawing moment and pitching moment of the head carriage in the WB case are 1.32, 1.26, 1.32, 1.57 and 1.52 times for the period of entry and 1.13, 1.24, 1.13, 1.42 and 1.69 times for the period of exit, respectively, compared with those in the AOT case. [ABSTRACT FROM AUTHOR]

Highlights • The differences in aerodynamic loads between the AOT and WB cases are revealed. • The running posture of each carriage is analyzed. • The response differences between the windward and leeward side wheels are revealed. • The safety of the HST in four running environments is evaluated. • The safety domain boundaries of the HST in four running scenarios are plotted. Abstract Windbreak (WB) and anti-wind open-cut tunnel (AOT) are two common windproof facilities for high-speed railways in windy areas. This study aims to conducts a comparison of the aerodynamic loads and corresponding traffic safety of both windproof facilities when the high-speed train (HST) passes through them under crosswind conditions. The aerodynamic loads are obtained via CFD simulation, and safety indexes are generated through the wind-train-track dynamic analysis system. The main common characteristics between AOT and WB cases are as follows. Firstly, the fluctuation amplitudes of the five aerodynamic loads of each carriage in two periods (i.e., entry and exit) are remarkably greater than those in other periods (i.e., running completely in crosswind or windproof facilities). Secondly, the sudden increase in the fluctuation amplitudes of the safety indexes is an important factor in the reduced safety of HST traffic, and the derailment coefficient (DC) of the head carriage is the key to control the safety of the entire HST. Thirdly, the existence of the ends of windproof facilities narrows the original safety domain scope of the HST running only in crosswind. The main differences between AOT and WB cases are as follows. Firstly, the maximum fluctuation amplitudes of the five aerodynamic loads of each carriage in the WB case are generally greater than the corresponding values in the AOT case, whether entry or exit, under the same conditions of train and crosswind speeds. Secondly, the scope of safety domain when the HST passes through the ends of the WB is considerably smaller than that of the HST passing through the AOT ends, and the AOT is more effective than WB in terms of windproof effects. Thirdly, for the high-speed railway in the windy area with AOT and WB, the safety domain boundaries V t = −6.3 V w + 343.3 and V t = −10 V w + 350 can be used respectively to provide a reference for traffic safety command. [ABSTRACT FROM AUTHOR]

Unilateral vertical noise barrier (UVNB), bilateral vertical noise barrier (BVNB) and fully enclosed noise barrier (FENB) are widely used along high-speed railways. The running safety of a high-speed train (HST) faces challenges when entering and exiting a noise barrier in crosswind. A series of computational fluid dynamics numerical simulations of train-noise barrier-crosswind based on the improved delayed detached eddy simulation model and 'mosaic' mesh technology are conducted. The influence of different noise barrier types on the aerodynamic load of the carriage is studied. Three buffer structures with different lengths are designed to alleviate the deterioration of aerodynamic performance of HST. Results shows that: The amplitudes of the lift force of the tail car, the lateral force and pitching moment of the head car in the BVNB are the largest, and the amplitude of the yawing moment of the head car in the FENB is the largest. Considering the engineering effects and economic benefits, a buffer structure with a length of six times head car length with a gradual ventilation rate is recommended for project, and the reduction rates of the change rates of the lift and yawing moment are 62.8% and 76.4%, respectively. • Aerodynamic characteristics of trains passing difference noise barriers are compared. • The graded air permeability end structures of three types of noise barriers are designed. • The buffer performance of end structures in noise barriers are analyzed. [ABSTRACT FROM AUTHOR]

High-speed trains (HSTs) often encounter crosswinds with complex pulsating components when running at a tunnel-bridge-tunnel section (TBTS), and their running safety may deteriorate sharply due to the complex terrain conditions in mountainous areas. This study aims to discuss the influence relationship of different turbulent conditions of the crosswind on the aerodynamic response of the HST passing through the TBTS. On the basis of the measured wind field data of a typical TBTS site, the pulsating wind field is numerically reconstructed by large eddy simulation, and the influence of the incoming flow dimension, the turbulence intensity and the average wind speed on the aerodynamic loads of the HST running at the TBTS are analysed. The corresponding influence mechanisms are explained in terms of the pressure distribution and flow field structure of the HST. The influence of the loading dimension of aerodynamic load and incoming turbulence intensity on the dynamic response index of the train body and wheel-rail contact is further discussed by establishing a wind-vehicle-bridge-tunnel coupling dynamic calculation model. The main conclusions are as follows: At the TBTS, the 1D pulsating incoming flow simulation scheme can be used rather than the 3D incoming flow scheme in calculating the aerodynamic response of the HST. The influence of the incoming turbulence intensity on the aerodynamic load of the HST is mainly reflected at the bridge section (BS), The fluctuation extent of the aerodynamic load of the HST increases with the increase in the turbulent intensity of the incoming flow. When the incoming flow turbulence intensity increases from 0 to 0.09, at the BS, the pitching acceleration of the train body and the vertical contact force of the wheel-rail on the leeward side increase by 18% and 16%, respectively. The average wind speed of the incoming flow has an important effect on the aerodynamic load of the HST, especially the head train, running at the TBTS. A linear positive correlation is found between the average wind speed of the incoming flow and the corresponding change amplitude of the aerodynamic load coefficient of the head train. When the HST runs at the TBTS, the five aerodynamic loads should be loaded in the calculation process of the aerodynamic response index of the HST, and the calculated wheel-rail response results are conservative when only two aerodynamic loads are applied to the train body. • The instantaneous vortex structures around HST running at the TBTS are investigated based on the LES method. • The pulsating wind field is reconstructed based on field tests. • A set of formulas are given to quantitatively describe the relationship between aerodynamic loads and average wind speeds. • The influence mechanism of incoming turbulence conditions on the aerodynamic response of the HST at the TBS is revealed. • The fluctuation of the HST aerodynamic load increases with the increase in the turbulent intensity of the incoming flow. [ABSTRACT FROM AUTHOR]

• The calculation scheme of aerodynamic load of HST is optimized. • The aerodynamic difference mechanism between the 'OUT' and 'IN' processes is revealed. • The interaction mechanism between resultant wind angle and jet flow is revealed. The running safety risk of a high-speed train (HST) deteriorates remarkably under crosswind when the train drives into a bridge from a tunnel (OUT) or from a bridge into a tunnel (IN). This study aims to reveal the difference in the aerodynamic performance of HSTs in the two processes in terms of transient aerodynamic loads and flow field. A calculation approach for aerodynamic loads in which the carriage surface is divided into segments in longitudinal and circumferential directions is proposed to obtain the real-life time history of aerodynamic loads. The main results can provide a theoretical basis for traffic safety command when HSTs run in an infrastructure scenario consisting of tunnel–bridge–tunnel (ISTBT). In the presence of crosswinds, the maximum fluctuation amplitudes of five aerodynamic coefficients in the processes 'OUT' and 'IN' are increased by 2.1–83.8 and 4.0–84.3 times, respectively. The fluctuation amplitudes of five aerodynamic coefficients in the process 'IN' are generally 1.01–2.32 times larger than those in the process 'OUT' in a crosswind environment. A large resultant wind angle causes the fluctuation amplitudes in the five aerodynamic coefficients in the process 'IN' to be larger than those in the process 'OUT'. The maximum fluctuation amplitude of aerodynamic coefficients in leading and tail carriages is the key to controlling traffic safety when HSTs run in ISTBT in a crosswind environment. [ABSTRACT FROM AUTHOR]