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Ground configurations are an essential part of rail vehicles during wind tunnel tests. Reasonable reproductions of the infrastructures are of significance for experimental accuracy. In this work, the effects of ballast length were numerically studied via improved delayed detached eddy simulation (IDDES). Three extension lengths of the ballast accompanied by a 1/8th three-unit train model were proposed, with a pseudo infinite scenario as the benchmark. The numerical algorithm was firstly validated through a wind tunnel test in terms of aerodynamic loads and pressure distribution. The results revealed that the extended length of ballast had a significant impact on the leading and tail cars while less affected the middle car, due to the relatively farther distance from ballast ends. Ignored the drag coefficient, the influence of the ballast length on the separate cars was that the aerodynamic coefficients predicted by much longer ballast got closer to the benchmark. The ballast-edge-induced unrealistic flow and the train-nose-tip-induced realistic flow could easily be merged and interacted with each other and reinforced, thus causing a noticeable low-velocity zone at the leeward side. With the increasing ballast length, those two separations gradually moved away from each other, decoupled, and receded. A minimum length of E/H = 2 is recommended considering the aerodynamic performance and practical constraints of wind tunnel width. This study provides potential guidance for the arrangement of ground configurations for rail vehicles during wind tunnel tests. [ABSTRACT FROM AUTHOR]

Wind tunnel tests for trains under large yaw angles are usually limited due to the width of the wind tunnel. Therefore, the leading car and a downstream dummy vehicle model are often employed instead of a real train, but there are no clear regulations regarding the shape of the end of the dummy vehicle. This paper studied the impact of the trailing edge shape of the downstream dummy vehicle on train aerodynamics subjected to crosswind based on the shear-stress-transport k-ω turbulence model of the delayed detached eddy simulation. Three types of end shapes, namely the rectangular end shape, the arc end shape, and the streamlined end shape were chosen for comparison, and the simulation results of the three-car-group train were selected as the benchmark. First, the reliability of the numerical method was validated by wind tunnel tests. Then, the aerodynamic coefficients under yaw angles of 0°–60° and the surface pressure distributions and flow structures around the train under the yaw angle of 60° of the head cars with different end shapes were compared and analyzed. [ABSTRACT FROM AUTHOR]

To reduce the impact of a mountain ridge on the crosswind flow field of a specific section of the Lanzhou-Xinjiang high-speed railway, a portion of the mountain ridge was removed to increase the distance from the windbreak. To verify the effects of this flow optimization measure, the wind speed and wind angle were tested in this mountain ridge region. In this paper, under the actual conditions of this specific case study, the average and transient wind characteristics were analyzed based on the test results. Then, based on the actual terrain model, using the computational fluid dynamics (CFD) method with two inlet boundary conditions, namely, constant wind and exponential wind, the results obtained from the two boundary conditions were validated. Furthermore, the visualized flow structures and wind speed distributions along the railway under both boundary conditions were compared. Finally, along the railway, the impacts of different terrain types on the flow field of the railway were compared. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of a wind barrier on the aerodynamic performance of a train–bridge system under crosswind using a numerical simulation method. The studied bridge is a long-span cable-stayed bridge with a flat steel box girder, located in Chongqing, China. The flow field around the train–bridge system with and without a wind barrier is numerically simulated. Wind barrier porosities varying from 10 to 60% are evaluated. The tricomponent coefficients of the train, bridge, and train–bridge system are obtained and investigated in detail. The effect of the wind barrier on the aerodynamics of the train–bridge system is revealed through the determination of the aerodynamic forces, pressure mapping, and flow visualization. The results show that a wind barrier successfully decreases the mean velocity above the girder and consequently decreases the drag force and moment on the train; however, the wind barrier also significantly increases the drag force on the girder. Therefore, installation of a wind barrier improves the running safety of the train but is detrimental to the wind resistance of the bridge. Additionally, the efficiency of the wind barrier depends on the porosity. A lower porosity improves the train safety but is more detrimental to the bridge safety. An optimal wind barrier porosity of 30% is obtained based on the aerodynamic forces of both the train and the bridge. Compared to a train–bridge system without a wind barrier, the drag force and moment on the train decrease by 66.1 and 62.9%, respectively; the drag force on the bridge girder increases to 0.86, and the drag force on the train–bridge system equals that without the wind barrier. [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]

This study investigated the aerodynamic performances of four trains with different nose lengths (4, 7, 9 and 12 m) under strong crosswind using the detached eddy simulation (DES) method. The variations in the aerodynamic force coefficients with different nose lengths were analyzed. The pressure distribution on the train surface, vortex development around the train, and velocity field variation around the train with increases in the nose length were compared and discussed. The results indicated that in a strong wind environment, the aerodynamic drag coefficient was largest for the tail car, whereas the side force coefficient, lift coefficient and roll moment coefficient were largest for the head car. When the nose length of the train increased from 4 m to 12 m, the total drag coefficient of the train decreased by 19.0% and the side force, lift and roll moment coefficient decreased by 10.6%, 21.7% and 7.3%, respectively. In the horizontal section of the train head part and tail part, the largest pressure coefficient decreased in a logarithmic manner with increases in the nose length. The nose length significantly affects the pressure coefficient on the windward side of the head car and the leeward side of the tail car. With an increase in the nose length, on the leeward side of the train, the shedding length and influence width range of vortex were reduced; the strength of the spiral shedding and interaction effect of two vortices in the rear nose weakened, and their distinction was more notable, meanwhile, the wake impact ranges in the vertical and longitudinal directions decreased. [ABSTRACT FROM AUTHOR]

• The pressure integral method 15–4 is for the head car and tail car. • The pressure integral method 14–4 is for the middle car. • The error of M x of head car is less than 10% at different yaw angles. • The error of M x of tail car is less than 15% at different yaw angles. The present work studies the aerodynamic loads of a train for different yaw angles from 5.87° to 30° by using the detached-eddy simulation (DES) method. Furthermore, based on the pressure integral method, a reasonable layout of the pressure taps on the train under a crosswind is studied to obtain the aerodynamic forces and moments that are used for a comparison with the results of the wind tunnel test. Considering the lower errors of the pressure integral results and fewer number of pressure taps comprehensively, the pressure integral method in the case of 15–4 (15 represents the tap quantity along the length direction, 4 represents the tap quantity along the height/width direction) on the head car and tail car, the case of 14–4 on the middle car are relatively good among the nine cases discussed in this paper. Compared to the results of the wind tunnel test, for the head car, the maximum error of the side force coefficient (C y), rolling moment coefficient (M x), and yawing moment coefficient (M z) is all less than 10% for yaw angles from 5.87° to 90°, and the maximum errors of lift force coefficient (C z) is less than 20% for yaw angles from 10.2° to 90°; for the middle car, the maximum error of C y is less than 20% for yaw angles from 5.87° to 90°, and the maximum error of C z , M x and M z is all less than 15% for yaw angles from 5.87° to 90°; for the tail car, the maximum error of C y , C z , M x and M z is all less than 15% for yaw angles from 10.2° to 90°. [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 present work mainly focuses on the evolution of the airflow passing embankments of different heights, with and without trains. Using the delayed detached-eddy simulation (DDES) method, the effects on the velocity and acceleration of the airflow caused by the embankments' upstream slope were studied using a set of embankments with different heights. The aerodynamic loads experienced by each car of the train, on both the windward and leeward rails, were calculated and the effects of different embankments examined. To distinguish how the geometry of embankments affected the flow patterns, distributions of streamline, velocity and the vortices formed around the head car and embankment are shown. The differences in pressure distribution on central loops of each car caused by the different embankment heights were analyzed at a yaw angle of 19.8°. Using the wind speed at 4 ​m above the actual rails and the reference at 10 ​m above the ground, the effect of wind speed on the aerodynamic forces and moments of the train, independent of the embankments' height, can be obtained. This method has the potential to simplify the calculations needed to evaluate the safety of trains running on different embankment heights in strong wind environments. • Evolutions of the airflow passing embankments of different heights were compared and analyzed. • Variations in the form of the growth laws for different cars above these embankments were found. • A relationship was established between the wind speeds in two different measuring points. [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 present work focused on the aerodynamic performance of double unit trains (DUT) and traditional single unit trains (SUT) under crosswinds. The aerodynamic coefficient as well as the characteristics of the time-averaged and instantaneous flow of the SUT and DUT were calculated using the improved delayed detached eddy simulation (IDDES) method for 1/8th scale models. The numerical results were verified by wind tunnel tests. The time-averaged flow pattern on different cross-sections and horizontal planes were compared for the SUT and DUT. The pressure coefficients on the loops of different cars were also analyzed quantitatively. The vortices around the SUT and DUT were visualized, and the frequency characteristics of each car of the SUT and DUT were computed. The coupling region changed the forces on the train and increased the overall drag of the train. Faster vortex development was found on the last three cars of the DUT. Furthermore, a higher velocity belt was generated by the gap of the coupling region. The coupling region gave a significant influence of the power spectrum densities (PSD) on the last four cars and a relatively slight impact on the first two cars. • The aerodynamic forces of double unit trains under crosswind. • Leeward time-averaged flow patterns projected on different y-z planes. • Velocity distribution on horizontal planes of at different heights. • Ringed Pressure coefficients on train surface along the train length. • Different instantaneous characteristics between the SUT and DUT. [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]

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]

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]

Flow fields around reformed earth embankment windbreak walls (REEWWs) with five different porosities under crosswind were studied using the improved delayed detached eddy simulation (IDDES) based on the SST κ-ω turbulence model by computational fluid dynamics (CFD) in this paper. Based on the simulated flow field results, the finite element method (FEM) was adopted to analyze the wind-induced displacement of the catenary. The spatial dimensions of the five REEWWs were identical, but they had different porosities, with values of 0%, 12.5%, 25%, 37.5%, and 50%. The three-dimensional effects of the porosity on the flow structures and streamline patterns around the REEWWs and catenary, and wind-induced displacement of the catenary were investigated. The numerical algorithm used in this study was verified with the results from field tests. The results showed that installing a porous windshield on the top of the earth embankment windbreak wall will change the original flow structures. The windshield with a porosity of 37.5% reduced the wind speed around the catenary by 61.25% for line1 and 89.36% for line2, and the displacement of the catenary was reduced by 96.86%. Therefore, the protection performance of the catenary was improved. • Differences on the flow patterns around the windbreak wall and catenary were shown. • Velocities around the catenary under different porous windbreak walls were analyzed. • Turbulence intensity and gusts were investigated and compared. • Wind-induced displacements of the catenary were obtained and analyzed. [ABSTRACT FROM AUTHOR]