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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]

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]

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]

Based on unsteady simulations and decomposed sliding mesh technology, train aerodynamic and dynamic behaviors near an elongated hillock beside a windbreak under a crosswind were analyzed. First, the sudden deterioration of the aerodynamic performance was explained. Then, a mitigation measure was proposed to reduce the impact of the elongated hillock on the train. Finally, the dynamic responses for the original elongated hillock and mitigation measure were compared. The results showed that two symmetric vortices along the railway were generated by the elongated hillock, and in the position between these two vortices, a strong wind speed occurred, which resulted in a sudden impact on the train, and the aerodynamic impacts were the largest on the head car. A certain distance from the elongated hillock to the windbreak could make a mitigation effect. For the original elongated hillock, there was a severe yawing phenomenon of more than 83 mm/3° from the centerline of the car body for the head car. For the mitigation measure, the safety index and vibration displacement of the head car and tail car decreased effectively. • The train aerodynamic performance and flow deterioration mechanism were studied under the sudden elongated hillock area. • Based on the causes of the deterioration of the flow field, effective mitigation measures were proposed and investigated. • The system dynamic behaviors of the train under the original and the mitigation scheme were analyzed and compared. [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 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]

• 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]

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]

• Full-scale tests were carried out on a fast streamlined train in crosswinds. • Aerodynamic loads were obtained by discrete integration of pressure differences. • Means and fluctuations of aerodynamic loads were obtained by data processing. • Fluctuations of aerodynamic coefficients are due to oscillations of wind speed. • Dominant frequencies of aerodynamic coefficients are at Strouhal numbers of 0–0.4. Unsteady aerodynamic loads have a significant influence on the running safety of a train in crosswinds. Full-scale tests were carried out to measure the pressure on a fast streamlined train in crosswinds, and the unsteady aerodynamic loads were obtained by the discrete integration of the pressure to assess the influence of different crosswinds on the loads. The maximum wind speed was 34.0 m/s in the full-scale tests, and the maximum turbulence intensity was 0.202. The means and fluctuations of the side force coefficient, lift coefficient, and rolling moment coefficient around the lee rail at different yaw angles were studied. The means first increased and then decreased with the increase in the yaw angle, and the maximum values occurred in the range of 54.5°–59.6°. The coefficients of variation of the aerodynamic load coefficients were approximately twice the turbulence intensity, which indicated that the fluctuations of the aerodynamic load coefficients were due to the oscillations of the wind speed. For the frequency characteristics of the aerodynamic load coefficients, the most dominant frequencies were at Strouhal numbers of 0–0.4. [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]