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The high-speed railway bridge, accounting for over 50% of railway lines, plays an important role in high-speed railways. When the train runs at high speed on these bridges, the strong winds will directly pose a risk to the safety of train operation, even causing train overturning accidents. Therefore, it is significantly urgent to accurately simulate the relative motion of the train-bridge system in crosswind environment. An improved delayed detached-eddy simulation study based on the shear stress transfer k-omega (I-ω) turbulence model was used to analyze the aerodynamic characteristics of trains running on bridges under two relative motion modes, i.e., the static synthesis method (SSM) and the dynamic decomposition method (DDM), and the variation rule of train aerodynamic loads. The differences of aerodynamic forces, surface pressure distributions, and flow characteristics around the train body under two motions were discussed. The results show that the applied velocity-inlet boundaries in two relative train-bridge motion modes under crosswinds lead to a large difference in the flow characteristics around bridges. Compared with the SSM, the DDM generates more small-scale vortices in the leeward side of the train, causes more disturbances, and enhances the flow instability. Under the DDM, the side force coefficient and lift force coefficient of the train are decreased by 1.99%, 66.67% (Train on the windward side) and 24.47%, 48.24% (Train on the leeward side), respectively, as compared to the SSM. The achievements obtained in the current study can provide data support for the operation standard of high-speed trains traveling on bridges. [ABSTRACT FROM AUTHOR]

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]

• A moving model system of the HST-noise barrier is established. • Fully- and semi-enclosed city-oriented noise barriers are compared. • The temporal and spatial characteristics of the aerodynamic pressure are compared. • The dominant frequency of the train-induced aerodynamic pressure is investigated. Two types of city-oriented noise barriers, i.e., fully-enclosed noise barrier and bilateral inverted l -shaped semi-enclosed noise barrier, have been gradually adopted in city centres along high-speed railways to reduce noise pollution. The aerodynamic impacts of high-speed trains present a threat to the long-term durability of the city-oriented noise barriers. To promote the usage and increase the sustainability of city-oriented noise barriers, a moving-model experiment system with city-oriented noise barriers and HST with a scale ratio of 1:16.8 is established. The train type is CRH380A and the train speed is up to 350 km/h. A systematic comparative study on the aerodynamic performance of the two types of city-oriented noise barriers is conducted. The similarities and differences of transient pressure time–histories, spatial distribution of pressure peaks and spectral characteristics of aerodynamic pressure acting on the two types of noise barriers are compared and discussed. Moreover, the influence of train speed on the characteristics of the train-induced aerodynamic pressure is also investigated. The results show that the pressure fluctuation of the two types of noise barriers is caused by different reasons. Compared with the fully-enclosed noise barrier, the transient pressure of the semi-enclosed noise barrier is more sensitive to train speeds. The research results may provide a reference for the engineering design of city-oriented noise barriers on high-speed railways. [ABSTRACT FROM AUTHOR]

In this study, the effect of the freight train formation on the train aerodynamic performance was studied. Six cases involving a locomotive (LM) and three different freight vehicles – a boxcar (BC), a tanker (TK), and a double-container freight wagon (DW), were compared and analyzed. The results showed that the aerodynamic drag was significantly affected by the freight train formation type, and the total drag force in Case 2 (LM + BC + DW + TK) was the smallest. Furthermore, the flow field around the train was analyzed to reveal the influence mechanism of the different types of freight train formations on the aerodynamic drag. The car position and the adjacent cars had significant effects on the aerodynamic characteristics of the train. The DW had a greater effect on the pressure and velocity distributions around the train. In addition, the variations of the vortices in the near wake of the same tail car were inconsistent, although there were similar characteristics for the same tail car. [ABSTRACT FROM AUTHOR]

Field tests were carried out to measure the wheel-rail forces of a high-speed train passing by a windbreak breach with a crosswind speed and a train speed of 32 m/s and 120 km/h, respectively. Unsteady Reynolds-averaged Navier-Stokes simulations and multibody dynamic simulations were carried out to reproduce the field test experiments. The results obtained indicated that the side force and yawing moment of the train plays a key role in the safety of the head and the tail of the train when it passes by a windbreak breach. By analysing the flow structures, the reasons behind the different aerodynamic loads on the train head and tail were discussed. Based on the vehicle movement, the maximum derailment coefficient (0.8) of the train head appeared to be at a higher risk of danger as compared to the maximum derailment coefficient (0.2) of the train tail. This is due to the wind loads on the train head which compel the bogies to relatively move with the carbody along the lateral direction one more time than the train tail. Whereas, for the train tail, there is no relative motion between the carbody and bogies on the tail. [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]

A certain gap spacing between adjacent vehicles is usually inevitable in wind tunnel force tests of high-speed trains under no crosswind, which may affect the wind tunnel test results. Thus, to understand the influence of gap spacings on the train aerodynamics, the aerodynamic drag, pressure distributions and airflow structures of 1/8th-scale high-speed train models with gap spacings of 0, 5, 8, 10, 20, and 30 mm were studied using RANS based on SST k-ω turbulence model. The simulation method was verified by the wind tunnel experiment data. The results show that the gap spacing significantly affects the airflow structure around inter-car gap and aerodynamic resistances of train models. For the high-speed train model scaled at 1/8th at zero yaw, compared with gap spacing of 0 mm, the gap spacings lead to a significant reduction in the aerodynamic drag of the head car and an increase in that of the tail car, whereas which of the middle car is not significant. The maximum difference of the drag coefficient of the entire train model is smaller than 2.0%. When the gap spacing does not exceed 8 mm, the discrepancies of the drag coefficients of three cars are within 6.15%. [ABSTRACT FROM AUTHOR]

In this study, the time-averaged and instantaneous slipstream velocity, time-averaged pressure, wake flows, and aerodynamic force of a high-speed train (HST) with different nose lengths are compared and analyzed using an improved delayed detached-eddy simulation (IDDES) method. Four train models were selected, with nose lengths of 4, 7, 9, and 12 m. To verify the accuracy of the numerical simulation results, they were compared with wind tunnel test results. The comparison results show that the selection of the numerical simulation method is reasonable. The research results show that with increasing nose length, the peak values of the time-averaged slipstream velocity of the trackside position (3 m from the center of track and 0.2 m from the top of rail) and the platform position (3 m from the center of track and 0.2 m from the top of rail) decrease continuously, and show a trend of rapid reduction at first, and then a slow decrease. As the nose length increased from 4 to 12 m, the time-averaged slipstream velocity at the trackside position and platform position are decreased by 57% and 19.5%, respectively. At a height of 1.6 m from the top of the rail, ΔCPmax (maximum pressure coefficient), |ΔCPmin| (the absolute value of minimum pressure coefficient), and ΔCP (pressure change coefficient) decrease with increasing nose length, which is similar to the peak value of time-averaged slipstream velocity, decreasing rapidly at first and then slowly. As the nose length increased from 4 to 12 m, decreases of ΔCPmax, |ΔCPmin|, and ΔCP by 26.5%, 58.5%, and 44.8% were shown, respectively. Different nose lengths also have a significant impact on wake flow. [ABSTRACT FROM AUTHOR]

In areas with strong wind, windbreaks are built along railways to reduce the impact of wind on trains. However, because of the restrictions imposed by actual terrain, windbreak structures are often not uniform, such as from a cutting to an embankment, resulting in a discontinuous transition region. When a train runs through this region, a distinct yawing phenomenon occurs. This study numerically explored the aerodynamic features of a train running through a rectangular windbreak transition region. The variations in the pressure, side force, and moment of a train were analyzed, and the flow field features were clarified. Furthermore, the yawing motion of the car body with time was described. Finally, based on EN14067-6, the critical wind speed was obtained using the safety assessment of a train running through a windbreak transition region. [ABSTRACT FROM AUTHOR]

With increasing train speeds, the wind environment along routes has become complex, variable, and extreme. Constructing windbreak facilities is an effective strategy to enhance train operational safety in windy zones. Various windbreak designs exhibit notable differences in improving train dynamic performance, and economic considerations are also crucial. Utilizing the non-constant compressible Reynolds time-averaged equation URANS (Unsteady Reynold-averaged Navier–Stokes) alongside the shear-stress transport (SST) k-ω turbulence model, this study simulates the non-constant aerodynamic characteristics of a 350 km/h high-speed train traversing through different forms of windbreak corridors in a 30 m/s wind zone. The train's dynamic response was captured using a combined CFD–MBD (Computational Fluid Dynamics and Multi-Body Dynamics) offline time-domain simulation, the accuracy of which was verified experimentally. Results indicate that vortices of various positions and shapes form in the flow field along the windbreak corridor depending on the size of the openings. Using the no-windbreak corridor (Case 1) and the fully enclosed corridor (Case 4) as control groups, it was observed that smaller openings lead to more stable airflow, enhancing peak damping and fluctuation effects, albeit with varying stages of aerodynamic load fluctuation. The 1/3-opening windbreak corridor (Case 3) effectively mitigated the sudden aerodynamic load changes at the wind zone transition of the 2/3-opening windbreak corridor (Case 2), with the primary fluctuation area in Case 3 being the wind section. Dynamic analyses revealed that Case 2 exhibited insufficient lateral aerodynamic performance, raising derailment concerns. In contrast, Case 3 ensured travel safety and comfort effectively, while Case 4 offered excessive protective capacity. This study's findings serve as a valuable reference for designing windbreak corridors and ensuring the safe operation of trains in windy regions. • The internal flow field varies with the opening size of windbreak corridors. • Peak and fluctuating aerodynamic loads depend on opening size of windbreak corridors. • The abrupt change of wind load is the largest in the transition area of windbreak corridor. • The aerodynamic load impact of the head car is the largest. • Lateral aerodynamic performance of maximum opening windbreak corridor is insufficient. [ABSTRACT FROM AUTHOR]

Double-unit trains composed of the same type of high-speed trains (HSTs) are relatively common. The connection of different types of trains, however, has been rarely studied. Therefore, we adopted an improved delayed detached-eddy simulation (IDDES) method to investigate the aerodynamic characteristics on double-unit trains formed by different types of HSTs. Two standardized HSTs—Train A and Train B at present in China—are used to form four different cases (A-A, A-B, B-A, and B-B). We conducted algorithm validation and grid independence to ensure the reliability of numerical results. The results showed the drag of case B-B was smaller when the same HST units were connected, whereas the drag of case A-B was smaller when the different HST units were connected. Downstream the coupling region, the structures of vortex shedding presented obvious differences for each case, which further led to different fluctuation intensities in wake vortices. The order of the height of the wake vortices was as follows: h 1(A-A) > h 3(B-A) > h 2(A-B) > h 4(B-B). The tail of the upstream vehicle had a dominant influence on the slipstream peak in the coupling region. • The minimum drag of double-unit train formations with different combinations is obtained. • The discontinuous coupling region has an obvious influence on the downstream vortices. • The tail of the upstream vehicle has a dominant influence on the slipstream peak in the coupling region. [ABSTRACT FROM AUTHOR]

Crosswind stability of trains is significantly affected by running safety and pantograph–catenary interaction, which are dependent on the depths of railway cuttings. Under crosswind with wind speed of 30 m/s and yaw angle of 30°, the aerodynamic loads and surrounding flow of the train and pantograph in the cuttings with different depths (0, 3, 6, 9, and 12 m) were investigated using numerical simulations. A dynamic model of the pantograph–catenary interaction was established and employed to analyze the contact force. The head car was the most critical even after accounting for the pantograph under crosswind. The head car was better protected against crosswind as the cutting became deeper. The pantograph–catenary interaction was optimal in the cutting with a depth of 6 m. The time-averaged contact force was excessively large in the shallow cutting, whereas the contact loss occurred in the deep cutting. The depth of the cutting had a different effect on running safety and pantograph–catenary interaction. Hence, a balance between the running safety and pantograph–catenary interaction should be considered in the cutting. According to the fitting results, the appropriate range of cutting depth is 4.6–6.5 m. Overall, these conclusions provide insight into the effect of cutting depths on the crosswind stability of trains and indicate the importance of the pantograph–catenary interaction in the design of railway cuttings. • The effect of railway cutting depths on crosswind stability of trains was studied. • The crosswind stability of the train was assessed by numerical simulations. • The running safety improved with the increase in the depth of the cutting. • A medium depth of the cutting was beneficial for the pantograph-catenary contact. [ABSTRACT FROM AUTHOR]

The harvesting of wind energy from the slipstream generated when a train passes through a tunnel is a new way to produce renewable energy. From the perspective of CFD (Computed fluid dynamics), a three-dimensional URANS (unsteady Reynolds-averaged Navier–Stokes) model was used to study the energy harvesting performance of wind turbines with different design parameters inside the tunnel during the entire process of a train passing through a tunnel. A higher value of offset distance of blades could promote the power efficiency of the wind turbine inside the wind tunnel. The maximum power efficiency with regard to overlap distance was found when an overlap distance is 0 m. The turbine with a negative twist angle yielded a better performance than the turbine with a positive twist angle. The optimal wind turbine can generate up to 157.9 W power when a train passes at 350 km/h. Given the tunnel distribution in China, 4.8 × 1012 J energy will be recovered each day by this way, which is sufficient to supply the emergency power for railway lighting. It can also effectively ease the pressure of daily lighting power in railway tunnels. • Harvesting wind energy from railway tunnels is considered feasible. • DFBI (dynamic fluid body interaction) was used to simulate the response of the turbine. • The power efficiency of turbines with various design parameters was quantitatively evaluated. • The optimal wind turbine can generate up to 157.9 W power when a train passes at 350 km/h. [ABSTRACT FROM AUTHOR]

The train-induced airflow in a tunnel has great significance for tunnel ventilation, fire rescue, and equipment installations. In particular, the aerodynamic effects induced by two trains passing each other in a tunnel are fiercer and complicated than those of a single train. In this research, a comparative CFD study of the three-dimensional slipstreams induced by a single train and two trains passing by in a tunnel was conducted using the unsteady Reynolds-Averaged Navier–Stokes (URANS) method. Three-dimensional computational models of a high-speed train and a tunnel are developed based on the sliding mesh technique and validated through experiments. The characteristics of the components of the slipstream were fully reported in three directions at different spatial positions. The results demonstrated that the impact of the tunnel pressure waves on the local airflow was independent of the spatial locations for the same cross-section. The variations of the longitudinal component (u) and the resultant slipstream (U R) were generally consistent with each other, demonstrating that the slipstreams inside the tunnel were mainly longitudinal flow. In addition, the piston effect was more pronounced when the space was constrained by another train for the crossing-trains case. The largest discrepancy of the maximum peak value at different positions for the crossing-trains case was 34% larger than that of the single-train case. • The time and spatial evolution of the slipstreams when two trains meeting in a tunnel were numerically investigated. • The distribution of the slipstreams with longitudinal, vertical and lateral distance were comparatively presented. • The relationship between the pressure waves and slipstreams was fully analyzed. [ABSTRACT FROM AUTHOR]

The geometries of bogies have a significant influence on the aerodynamic performances of high-speed trains (HSTs) in crosswinds, especially for wind tunnel tests. The delayed detached-eddy simulation (DDES) method was used to calculate the aerodynamic characteristics of 1/8th scaled HST models with differently simplified bogies under crosswinds. The numerical results were verified by wind tunnel tests using a same model. It was proven that the complexity of bogies has a significant influence on the HST models' aerodynamic drag and rolling moment at various yaw angles. The flow field of the HST models under a 30° crosswind was then employed to study the effects of the bogies. With the simplification of the bogie structure, the positive and negative pressure in bogie cabins increased while that on the top surface seldom changed. Various flow patterns were found on the windward side and top surface of bogie cabins. The differences of the flow fields underneath the train models were quantitatively analyzed using the vertical velocity profiles near each bogie. • Aerodynamic drag and rolling moment caused by various bogies under crosswinds. • Pressure distribution on bottom and top central line of train bodies. • Differences on flow patterns on boards of bogie cabins. • The underbody flow in term of velocity profiles vary due to bogie complexity. [ABSTRACT FROM AUTHOR]

The train/tunnel aerodynamic effects still remain a major concern during high-speed railway construction. At present, different sizes of tunnels with constant cross-section are generally adopted based on train speed and blockage ratio. However, for tunnels with constant cross-section, narrower cross-section leads to worse aerodynamic effects while larger cross-section results in sharply increasing costs. Focusing on this problem, this paper proposes a new type of high-speed railway tunnel to mitigate the aerodynamic effects by enlarging the cross-section at both ends and reducing the cross-section in the middle portion of the tunnel. A three-dimensional, unsteady, compressible and RNG k-ε turbulence model is utilized to simulate the pressure waves induced by a high-speed train passing through such a tunnel. Three cases with different enlarged portal lengths are simulated. The pressure variations on the tunnel wall and train surface are compared with previous moving model tests to validate the numerical algorithm. The results show that the train-tunnel-entry induced pressure transients are greatly reduced compared with that of constant cross-section tunnel. In addition, the pressure gradient and micro-pressure wave (MPW) emitted from the tunnel exit are also considerably decreased. Due to the enlarged portal of the tunnel, pressure waves are repeatedly reflected, and a new compression wave is developed at the junction where the tunnel cross-section abruptly changes. As a result, the wave energy is dissipated, and its strength is reduced. However, it is revealed that the length of the enlarged portal has less influence on the maximum pressure gradient and the MPW. • A new type of high-speed railway tunnel with cross-section expansion is proposed. • The propagation characteristics of the pressure waves are fully analysed. • Influence of the enlarged portal length on pressure variations is numerically investigated. • Pressure distributions on tunnel wall and train surface are performed. [ABSTRACT FROM AUTHOR]

• Changepoints and piecewise linearities of pressure on trains were evaluated. • A strategy of discretization based on Lagrange rectangular elements was suggested. • A strategy of discrete integration was presented to measure aerodynamic loads. • The strategies can be used in full-scale tests and model tests. • The strategies can accurately obtain means and fluctuations of aerodynamic loads. Discrete integration occupies an important place in train aerodynamic tests in crosswinds. Improved delayed detached eddy simulations based on shear stress transport k - ω turbulence models were carried out to calculate the side force, lift, rolling moment around the lee rail, and surface pressure on bluff and streamlined vehicles. The changepoints and piecewise linearities of the pressure coefficients were evaluated, and the maximum coefficient of determination in the elements was 0.9973. A realizable strategy of the discretization based on the Lagrange rectangular elements was suggested, including the largest lengths and numbers of the elements. From this, a strategy of the discrete integration was presented to measure the aerodynamic loads, considering the real orientation of the elements. The maximum errors of the mean aerodynamic load coefficients of the bluff and streamlined vehicles were 4.1% and 2.2% (except the mean lift coefficient of the bluff vehicle), respectively. The errors were less than those in the previous studies, especially for the streamlined vehicle, which reduced by up to 8.7%. The unsteady aerodynamic loads with no delay obtained by the strategies were near to natural ones in the frequency range that people would be concerned about in crosswinds (at the Strouhal number of less than 0.4). Some suggestions were made for using the strategies in the full-scale tests and model tests, which provided a foundation for further studies of the running safety in natural crosswinds. [ABSTRACT FROM AUTHOR]

Determining the dynamic airtightness coefficient (τ d y n ) of train carriages using a high-accuracy and high-efficiency method is essential regarding the study of the dynamic airtightness performance of high-speed trains (HSTs) traveling through tunnels. This study set out to provide a systematic elaboration and investigation of the whole process of establishing the calculation methodology of τ d y n of HST carriages. Moreover, the applicability of three different typical optimization algorithms in the calculation of τ d y n was explored and compared. These were the traversal algorithm (TRAA), the trichotomy algorithm (TRIA), and the genetic algorithm (GA). Using the established calculation method, the values of τ d y n of different HST carriages for tunnels with different lengths were calculated based on field test data of pressure outside and inside HST carriages. Results revealed that the selection of optimization algorithms had significant effects on the calculation process of τ d y n because of their different optimization mechanisms. These three optimization algorithms were proven to be feasible for establishing the calculation method of τ d y n and gave the same calculation result of τ d y n for the calculation example within the expected accuracy. The elapsed time of the TRAA and GA were approximately 100 and 80 times that of the TRIA regarding the calculation example. The TRIA was the preferable choice for the calculation of τ d y n among the three algorithms because of its uncomplicated implementation logic and high efficiency. Within the tunnel-length range involved, the tunnel length itself had no significant effect on τ d y n of HST carriages. A significant increasing trend in τ d y n of HST carriages was found along the train length. Compared to the head car, the increasing ratio of τ d y n of the second car was varying from 0.2 to 0.5, while the increasing ratio of the seventh car was ranging from 0.8 to 1.7 considering different tunnel lengths. These findings provide a reference basis for the design of the calculation method of τ d y n of HST carriages and also enhance understanding of τ d y n of HST carriages under different operating circumstances. • The whole process of establishing the calculation method of the dynamic airtightness coefficient of trains was elaborated. • Different calculation methods of dynamic airtightness coefficient were established based on three optimization algorithms. • The effect of tunnel lengths on the dynamic airtightness coefficient of high-speed train carriages was investigated. • Differences in dynamic airtightness coefficient among different train carriages were discussed. [ABSTRACT FROM AUTHOR]

The effect of windbreak wall types on their windproof effects on trains has been systematically investigated by comparing the flow field around a high-speed train behind three typical windbreak walls. These three typical windbreak walls are widely used along the windy railway lines in China, which include the earth embankment–type windbreak wall (EW), the road cutting–type windbreak wall (RW), and the straight reinforced concrete–type windbreak wall (SW). We compared the time-averaged crosswind-induced flows and aerodynamic performances of high-speed trains behind these three windbreak walls with the same height using numerical simulations. The results revealed that the windbreak wall geometric shape effects on the aerodynamic load coefficients varied according to the type of aerodynamic load and carriage marshalling positions but barely varied with yaw angles. The total drag coefficients of the train in the EW and RW were approximately 50–60% of that in the SW under the two smaller yaw angles and were only 30–40% for the largest yaw angle. For the absolute value of the side force and rolling moments coefficients, the maximum values for the head and middle cars both appeared in the RW, and the corresponding minimum values were obtained in the SW. The maximum and minimum values for the tail car were obtained at the SW and EW, respectively. The maximum of the rolling moment coefficient among three carriages in the SW was approximately 45–60% of that in the EW and only 30–40% of that in the RW. The time-averaged train surface pressure coefficient and flow patterns were similar between the EW and RW, which showed apparent differences from those in the SW. The SW provided a strong blocking effect on the incoming windward airflow and avoided the direct impact on the train. Compared with the RW, the uplifting effect of the EW's windward slope on the incoming flow further reduced the crosswind effect on trains. In addition, the dominating frequency characteristics of the aerodynamic loads were significantly affected by windbreak wall types. These findings provide a systematic understanding of the time-averaged aerodynamics of trains behind these three typical windbreak walls. • Simulations of crosswind-induced flows around high-speed trains behind three typical windbreak walls were conducted. • Time-averaged flow characteristics were analyzed for three different windbreak walls. • Train aerodynamic performances behind three typical windbreak walls were compared in detail. • The mechanism of windproof performance differences between three typical windbreak walls was systematically explored. [ABSTRACT FROM AUTHOR]

Wind tunnel tests on rail vehicles, especially the crosswind evaluation, are often used for the determination of critical wind characteristics. To increase the reliability of the wind tunnels for these requirements, correlation data between various wind tunnels is necessary. Along those lines, a wind tunnel campaign on a 1/20th high-speed train was conducted at three separated facilities, including the study of two floor configurations within the same wind tunnel. A symmetry check was made by monitoring pressure signals at both sides of the vehicle, and the load coefficients that fall within negative and positive yaw angles. The results show good consistency with aerodynamic load coefficients measured at separated wind tunnels. The standard deviation of C M x,lee increases with the yaw angle exponentially. Pressure taps for geometric transitions and suction peaks tend to have a larger level of symmetry discrepancies than other taps. Pressure distributions for longitudinal centerline and loops in all facilities have a similar trend, while the dispersion degree slightly differs in various regions. These differences are partly explainable by the experimental settings, i.e., the boundary layer development above the floor, the offset installation of the model, and the floor configurations. Therefore, special attention is suggested to be paid to the floor configurations and boundary layers above the floor when performing related experimental works. • The aerodynamics of the same train model is tested in multiple wind tunnels. • The load coefficients of the vehicle measured in different facilities show a good correlation. • The symmetry analysis of aerodynamic load and pressure distribution is presented. • Pressure discrepancies between multiple wind tunnels are revealed and potential reasons are analyzed. [ABSTRACT FROM AUTHOR]

High-speed railway lines are widely distributed worldwide. The surrounding wind environment of such railway lines is complex, which significantly affects the safety of high-speed train operations. Using a combination of the computational fluid dynamics method of improved delayed detached eddy simulation and sliding grid technology, the effects of one- and two-side windbreak walls on the unsteady aerodynamic performance of a high-speed train running under a crosswind on a double-track railway line with an embankment and the flow-field characteristics around the train were systematically studied. The grid independence and numerical methods used in this study were verified. The results showed that when the windbreak wall was absent, the aerodynamic performance of the train running on the upstream railway line was the poorest, while the train running on the downstream railway line exhibited large aerodynamic fluctuations. The windbreak wall significantly reduced the aerodynamic force and its fluctuation; the one- and two-side windbreak walls had different effects on the unsteady aerodynamic performance of trains running on the upstream and downstream railway lines under a crosswind. The one-side windbreak wall could restrain the aerodynamic fluctuation of the train more and is thus preferred from the perspective of construction effort and cost. • Effects of one- and two-side windbreak walls on the unsteady aerodynamic performance of a moving train under a crosswind were studied. • Aerodynamic performance of the train running on the upstream railway line was the poorest. • One-side windbreak wall restrain the aerodynamic fluctuation more and is preferred from the perspective of effect and cost. [ABSTRACT FROM AUTHOR]

• Impact of Mach waves on local pressures is greater than the slipstreams. • Undisturbed slipstreams derived from the Mach waves are free from the sectional positions. • Slipstreams on near side respond more intensively to the increase of blockage ratio. • Slipstream peaks along vertical and lateral directions more correlate for smaller blockage ratios. The train-induced airflow in a railway tunnel is of great significance for tunnel ventilation, fire rescue, and ancillary facilities overall. Previous research mainly focused on piston wind in metro tunnels, while the slipstream in high-speed railway tunnels is more drastic and complicated owing to the faster vehicle speed and diverse blockage ratios. In this research, a computational fluid dynamics (CFD) study was carried out to explore the three-dimensional transient airflow induced by a commercial high-speed train circulating through tunnels at 350 km/h under different blockage ratios (β = 0.175, 0.160, 0.140, 0.122, and 0.112). First, the train-tunnel model was established based on the unsteady Reynolds-Averaged Navier–Stokes (URANS) method merged with the sliding mesh technique, altogether validated with experimental evidence. Then, the resultant slipstream and the individual components were investigated, and it was concluded that the longitudinal component was dominant. The variation behaviors of the slipstream and local pressure with the different blockage ratios were comparatively obtained. Finally, the relationships between the slipstream and the spatial distance in longitudinal, lateral, and vertical directions were analyzed. This study provides a guideline for the determination of the tunnel clearance, and wind load evaluation in a high-speed railway tunnel. [ABSTRACT FROM AUTHOR]

Reasonable gap spacings between adjacent train vehicle models are of great significance for the data accuracy during a wind tunnel test. In this research, crosswind flows around 1/8th-scale high-speed train models with inter-carriage gap spacings of 0, 5, 8, 10, and 20 mm are studied using improved delayed detached eddy simulation (IDDES) with the SST (shear-stress transport) k-omega model. The numerical methodology is first validated against the wind tunnel experiment data. Then, the effects of gap spacings on aerodynamic loads and the flow field around the train are investigated. The results indicate that the side force of the tail car significantly increases with the gap spacing, in which the maximum difference occurs at 20 mm compared with the zero gap spacing, whereas the difference in the drag decreases. When the gap spacing is greater than 10 mm, the time-averaged pressure distribution, flow pattern and transient flow structures around the inter-carriage gap regions observe a significant difference from other gap spacings. Considering the overall aerodynamic effects induced by gap spacings and the practical handleability during a wind tunnel test, a gap spacing between 5 mm and 10 mm is therefore recommended for adjacent train vehicles with a 1/8th scale. • Time-averaged quantities of train vehicle models with different gap spacings were compared. • Flow patterns and structures around different gap spacings were investigated. • PSD of aerodynamic loads on train vehicles with different gap spacings was analyzed. • Reasonable gap spacings between adjacent train vehicle models were recommended. [ABSTRACT FROM AUTHOR]

• Trainset pressure on train surface is cut off by the tunnel gap. • Tunnel gap has significant influence on the slipstreams around the second tunnel entrance. • Aerodynamic force and moment coefficients nearly match for the first and second tunnel. • The aerodynamic issue of eliminating tunnel gap depends on their own critical tunnel lengths. This investigation deals with numerical solution of complex aerodynamic interactions induced by a high-speed train (HST) entering and passing through tunnels with a closely adjacent gap and without in between. We present evidences that included pressure transient on the train surface and tunnel wall and comparisons between slipstreams and aerodynamic loads. The results show that two closely adjacent tunnels with a gap does not induce pressure differences on the tunnel wall, in relation to pressures otherwise observed on the single long tunnel, but slightly affects the friction component of the initial pressure rise on the train surface. In addition, the peak values of the slipstreams on the side nearest to the train inside the second tunnel are larger than those recorded when the train passed the first tunnel, suggesting that the existence of a gap between tunnels affect the airflow within the second tunnel. Peak drag coefficients for the train travelling through the first and second tunnel match while being 9.8% lower than the corresponding value observed within a single yet longer tunnel. The study highlights the differences on train aerodynamics when in transit through closely adjacent tunnels and a long tunnel to conclude that improved aerodynamic performances should be considered as the train circulates through closely adjacent tunnels as opposed to through a single passage. The study provides an aerodynamic guideline and reference for the tunnel engineering. [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]

In this study, we analyse the unsteady flow around a 1/8th-scaled uniform vehicle model with three configurations of aerodynamic braking plates mounted at the inter-carriage region. In addition, the study aims at determining an appropriate plate configuration to obtain an increasing effect of aerodynamic drag and analyses the effect of plates on the flow field at the top of the vehicle, where a pantograph and an air-conditioning unit are installed. Improved delayed detached eddy simulations are conducted with shear-stress transport κ–ω turbulence model, and the results are compared with the experimental data and grid independence to validate the reliability of the obtained solution. Furthermore, the aerodynamic drag of the vehicles is significantly increased when the plates are opened and the aerodynamic braking distance is significantly decreased, especially for the single large plate mounted downstream of the inter-carriage region, followed by the single large plate mounted at the upstream of the inter-carriage region. In addition, the flow field around the inter-carriage region is more sensitive to the size of plates than their location. Both the pantograph and air-conditioning unit restrict the development of airflow downstream of the plates, and should thus be located as far away from the inter-carriage region as possible. Although the pantograph–catenary system would be affected by the opening of plates, the effect is not very large. The findings of this study can also be conducive to help engineers design and operate an optimal aerodynamic braking system. • Aerodynamic analysis was performed on a 1/8th-scaled train model with three plate configurations at the inter-carriage region. • The pantograph and air-conditioning unit restrict the development of airflow downstream of the plates. • Aerodynamic drag of the whole train is significantly increased by opening the plates. [ABSTRACT FROM AUTHOR]