Train Aerodynamics Research Articles

Effects of rail models on aerodynamic characteristics of trains in crosswinds at a large yaw angle

Rail models may be simplified at different levels in wind tunnel tests and numerical simulations. This work used delayed detached eddy simulations to analyze and compare the aerodynamic loads (drag, side force, lift, and rolling moment), surface pressure, and flow characteristics around a train model placed on subgrades with three different rail models: no-rail, simplified rail, and realistic rail. The simulations were conducted at a large yaw angle of 60°. The mean aerodynamic characteristics of the car bodies and bogies were similar with the simplified rail model and realistic rail model, while those were completely different without the rail model. The difference in aerodynamic loads between the no-rail model and the realistic rail model was as high as 53.1%, whereas the difference between the simplified and realistic rail models was only 7.7%. And for fluctuating aerodynamic characteristics of the train, there was still differences between the cases with the simplified and realistic models. Further, the rail model significantly impacted the flow (such as the velocity, turbulent kinetic energy, and vorticity) around the train, especially under the train, resulting in significant differences in the aerodynamic loads in time and frequency domains. For accurate and precise measurements of mean aerodynamic loads, incorporating a rail model (with the simplified model being sufficient) can improve accuracy by 48.0% and precision by 66.9%. When focusing on fluctuating aerodynamic loads, using a realistic rail model is essential to accurately capture amplitude-frequency characteristics. The rail model setup recommendations outlined in this work aim to enhance the accuracy and reliability of various wind tunnel tests and numerical simulations related to train aerodynamics.

Effects of windbreak types on aerodynamics of high-speed trains traversing from flat ground to semi-cutting and semi-embankment under crosswinds

Under the operation of strong crosswinds, the aerodynamic performance of high-speed trains (HSTs) will be seriously deteriorated when the transition section of flat ground and semi-cutting and semi-embankment (FGSCSE) is traversed, and the setting of windbreaks will help to slow down the impact of strong crosswinds on the trains. In this study, a three-dimensional coupled computational fluid dynamics numerical model to assess the aerodynamic performance of train–windbreak–FGSCSE–air system is developed. A comparative assessment is carried out to identify the variations in aerodynamic performance on the train carriage: no windbreak (NW), 50% ventilation windbreak (VW), and solid windbreak (SW), and the reasons for these variations are elucidated by examining the flow field structure's evolution. Furthermore, the operational safety of the train is discussed based on the indicator of wheel unloading ratio (fΔQ). Across the three distinct conditions, significant abrupt changes in aerodynamic load coefficients (ALCs) and the shedding of vortex structures are experienced by HSTs traversing the FGSCSE transition sections. Compared to the VW condition, the NW and SW conditions result in a greater number of shedding vortices on the leeward side and the tail of the train, and the VW condition results in the smallest magnitude of ALCs fluctuation. The power spectral density peak values of the aerodynamic loads follow the order: SW > NW > VW. Upon the train fully enters the subsequent operational environment, the VW condition has the smallest standard deviation of these coefficients. The standard deviations of CFy, CFz, CMx, CMy, and CMz for the head train in the VW condition are only 57.17% (46.81%), 55.85% (54.15%), 72.74% (34.62%), 57.99% (51.92%), and 44.60% (43.82%) of the corresponding values in the NW (SW) condition, respectively. In the NW, VW, and SW conditions, the fΔQ exceeds 0.9 when the wind speeds reach 30, 40, and 35 m/s, respectively. The windbreak with a ventilation rate of 30% performs the best, providing the most effective safety and stability for train operation.

Transient Analysis on the Crosswind Effect to the Aerodynamics of High-speed Train Travelled on the Bridge Between Two Tunnels at Jakarta -Bandung Track

The rapid evolution of global transportation technology is exemplified by Indonesia's innovative high-speed train initiative, linking Jakarta and Bandung in an impressive 45 minutes. Operating at 350 km/h, the HST CR400AF underscores the importance of aerodynamics in high-speed rail systems. This study delves into the significant impact of crosswind on key aerodynamic factors (drag, lift, rolling moment) within the tunnel-bridge-tunnel configuration. Leveraging Computational Fluid Dynamics (CFD) through ANSYS FLUENT, the analysis explores crosswind variations at 0 m/s, 10 m/s, and 25 m/s. Results reveal a proportional increase in aerodynamic load with higher crosswind intensities: 1.67 times for drag, 58.8 times for lift, and 29.8 times for rolling moment. Notable observations include pronounced aerodynamic load fluctuations during the "OUT" process, with the head section bearing the greatest load, followed by the tail and middle sections. These findings contribute valuable insights to the global discourse on enhancing safety and efficiency in high-speed rail systems

Study on the influence of intermediate airshafts on the aerodynamic effect of urban rapid rail transit

This study explores how intermediate airshafts affect the aerodynamics of urban rapid transit trains in tunnels. It employs a three-dimensional turbulence model to simulate train-tunnel interactions, specifically examining airshafts’ impact on transient pressure variations along surfaces. The model’s accuracy and reliability are confirmed by comparing results with full-scale experimental data. The results show that airshafts effectively mitigate peak tunnel wall pressures, with the lowest peak overpressure observed at the airshaft location. With the airshaft-reflected expansion wave arriving ahead of the train, the pressure between the train front and tunnel wall decreases compared to scenarios without airshafts. Similar transient pressure changes at the tunnel entrance and rear half suggest the emergence of a “secondary compression wave” due to the train’s transit.

Fighting wind with wind to improve high-speed train aerodynamics near mountains

A look at the acceleration effect of gale-force winds on high-speed trains reveals how mitigation efforts might be designed.

Kriging-based multi-objective optimization on high-speed train aerodynamics using sequential infill criterion with gradient information

For models with large numerical simulation costs, such as high-speed trains, using as few samples as possible to construct a high-precision surrogate model during aerodynamic multi-objective optimization is critical to improving optimization efficiency. This study proposes a sequential infill criterion (SIC) appropriate for the Kriging surrogate model to address this issue. Three multi-objective functions are employed to test the feasibility of constructing a surrogate model based on SIC, and the SIC surrogate model then performs multi-objective aerodynamic optimizations on the high-speed train. The findings indicate that the expected improvement infill criterion (EIC) in the first stage can enhance the global prediction accuracy of the SIC. An infill criterion based on EIC that fuses gradient information (PGEIC) in the second stage is proposed to seek samples in the Pareto front. The PGEIC surrogate model achieves the lowest generational distance and prediction error. The performance of EIC for global search, EIC for Pareto front search, and infill criterion for Pareto front search using only gradient information is poor. The final PGEIC–SIC surrogate model of train aerodynamics has less than 1% prediction error for the three optimization objectives. The optimal solution reduces the aerodynamic drag force of the head car and the aerodynamic drag and lift force of the tail car by 4.15%, 3.21%, and 3.56%, respectively, compared with the original model. Furthermore, sensitivity analysis of key parameters revealed that the nose height v1, cab window height v3, and lower contour line have a greater impact on aerodynamic forces. Moreover, the nose and cab window heights of the optimal model have been reduced, and the lower contour line is concave. Correspondingly, the streamlined shape appears more rounded and slender.

Analysis of the principle and applications of aerodynamics in high-speed railway

In recent years, high speed railway trains are a main part of modern transportation which brings extremely convenient. In this case, studies on aerodynamic performances and phenomenon of trains are the core for further development of high-speed trains. With this in mind, this paper briefly introduced aerodynamic formulae as well as summarized some major computational designs of train noses, with the corresponding experimental results of some designs. On this basis, the application of some designs was explained, with follow up limitations and outlooks of aerodynamics of high-speed trains. According to the analysis, results show that designs in China focus more on reducing aerodynamic drag, while the flatter design in Japan has a better overall aerodynamic performance. In addition, the limitations of current facilities as well as the prospects for the high-speed railway systems are demonstrated. Overall, these results shed light on guiding further exploration of high speed railway development.

Study on Lateral Vibration of Tail Coach for High-Speed Train under Unsteady Aerodynamic Loads

As the speed of high-speed trains increases, the vehicle’s lateral stability steadily deteriorates. There have been observations of abnormal vibrations in the tail car, particularly on certain sections of the railway line. This study built a high-speed train aerodynamic simulation model for a three-car consist, and a multibody dynamics simulation model for an eight-car consist based on numerical simulations of train aerodynamics and multibody dynamics. It investigated both steady and unsteady aerodynamic loads, flow field characteristics, and the dynamic performance of vehicles under varied aerodynamic loads at 400 km/h. The results indicate that the aerodynamic loads generated during high-speed train operation exhibit highly unsteady characteristics. Steady aerodynamic loads have a relatively minor impact on the vehicle’s dynamic performance, whereas unsteady loads exert a more significant influence. Under unsteady aerodynamic forces, the tail car experiences severe lateral vibrations. The lateral stability index, displacement, velocity, and acceleration of the tail car under unsteady conditions were measured at 2.26, 7.54 mm, and 0.53 m/s2, respectively. These values represent increases of over 17.71%, 148.84%, and 111.24%, respectively, compared to the steady loads. Large oscillation amplitudes result in more significant lateral displacements and accelerations of the vehicle. This phenomenon is a crucial factor contributing to the “tail swing” effect observed in high-speed trains. This study emphasizes the importance of considering unsteady aerodynamic effects in assessing the lateral stability of high-speed trains and highlights the significance of mitigating the adverse impacts of such dynamic responses, particularly in the tail car.

Dynamic Analysis of Moving Train Wake Vortex Under Different Infrastructure Scenarios Based on Modal Decomposition

Vortex shedding at the tail of a high-speed train changes the aerodynamic characteristics of the train, which affects the safety and stability of train operation. This paper takes CR400AF as the research object, and uses dynamic monitoring points to realize the whole process monitoring of the flow field at the tail of the train running in open air and in tunnel for the first time. The wake of the train in different infrastructure scenarios is analyzed by the proper orthogonal decomposition method. The study found that the wake vortex structure is quite different when the train runs in different scenarios, and the turbulent kinetic energy intensity of the wake in tunnel is higher than that of the open air running. Modal decomposition method can identify flow structures that have a large impact on train aerodynamics. Through frequency analysis, it is found that the modal frequency obtained from the decomposition is higher when running in open air than when running in tunnel. With the increase of train speed, the modal strouhal number increases when the train is running in open air, and decreases when the train runs in tunnel. After the train enters the tunnel, the reverse movement of the air around the train body suppresses the development and separation of the boundary layer, which is the main reason for the low frequency of wake vortex shedding in tunnel. The stability of the train running in tunnel is worse than that when running in open air, which is closely related to the more complex flow structure around the car body and the drastic change of aerodynamic force when running in the tunnel.

Investigating the effect of train speed and ground clearance on aerodynamics of a simplified high-speed train

Investigating the effect of train speed and ground clearance on aerodynamics of a simplified high-speed train

Contribution of computational wind engineering in train aerodynamics—past and future

Contribution of computational wind engineering in train aerodynamics—past and future

Numerical study of the trailing vehicle length on train aerodynamics under crosswind

Limited by the wind tunnel size, a one-and-a-half train model is generally adopted during the test to represent the realistic long tandem. Thus, the reasonable arrangement of the trailing vehicle length is of significance for experimental accuracy. In this work, the aerodynamic performance of trains with different trailing vehicle lengths subjected to crosswind was studied using the improved detached eddy simulation method combined with the shear–stress–transport k–ω turbulence model. The 1/8th scaled high-speed trains with five trailing lengths were proposed, and the aerodynamic differences were evaluated at yaw angles ranging from β = 0° to β = 60°. The numerical method was validated by the previous wind tunnel test. Results show that the aerodynamics and flow patterns of the La = 0.50 and the benchmark are highly relevant. The downstream dummy vehicle length has the greatest effect on aerodynamic coefficients at a higher yaw angle (β > 30°), especially at β = 60°, whereas the effects become insignificant at a lower yaw angle (β < 30°). For various La lengths, notable discrepancy appears at the leeward and top side where large vortexes shed off from the roof. The larger contributions to the lateral force and lift force coefficients are mainly due to these areas. A suitable length of La = 0.50 is therefore recommended to obtain more accurate aerodynamics of a long train set.

Influence of the Downstream Vehicle Length on Train Aerodynamics Subjected to Crosswind

Limited by the wind tunnel size, a short-length train model is generally adopted during the test to represent the realistic long tandem. Thus, the reasonable arrangement of the trailing vehicle is of significance for experimental accuracy.

A field study on the aerodynamics of freight trains with different stacking configurations

A full-scale 48-foot shipping container was instrumented with surface pressure taps and loaded onto a number of single- and double-stacked container freight trains. Surface pressure data enabled the container pressure drag coefficient to be evaluated for a range of different train loading configurations, container positions along the train, and atmospheric wind conditions. Field-based measurements show that for low and high crosswind conditions surface pressure distributions measured on the front face of the instrumented container are in good agreement with those reported in past studies. However, the magnitude of the pressure drag coefficient was found to be typically 50% lower for all loading cases analysed compared with previous seemingly analogous wind-tunnel and numerical investigations. For high crosswind conditions, the drag coefficient was found to increase and correlated well with the level of asymmetry observed in the measured pressure distributions. This was true for all cases regardless of the position along the length of the train. In the absence of direct information of the incident free-stream wind conditions, the level of asymmetry in the pressure distributions was found to provide a viable indirect method for assessing the impact that crosswinds have on the aerodynamic drag of freight trains.

Impact of ballast length on train aerodynamics for a wind tunnel layout via CFD analysis

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.

Effects of wind-rain coupling on the aerodynamic characteristics of a high-speed train

Simultaneous effect of crosswind and rainfall on railway vehicles has raised concern lately as it threatens the operational safety. In this study, the wind-rain coupling effects on the train aerodynamics have been systematically investigated by means of Euler-Lagrangian approach. The aerodynamic computational model is established based on non-spherical raindrops, and model verification is conducted with the aid of existing measurement results. The flow features as well as the train aerodynamic coefficients under wind-rain environments are systematically studied. The results show that, the mass concentration of raindrops around a train increases with rainfall intensity. The aerodynamic coefficients show linear relationship with the increase of rainfall intensity. Unlike that of a crosswind condition, train aerodynamic coefficients exposed to combined wind and rain are dependent not only on train shape and yaw angles, but also on resultant wind velocity and rainfall intensity. The formulae for predicting the aerodynamic coefficients of the train operating in wind-rain environments are finally obtained in this paper.

Aerodynamic influences of typical windbreak wall types on a high-speed train under crosswinds

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.

Numerical Investigation on the Flow underneath a High-Speed Train of Six Coaches Marshalled with Different Bogies

The turbulent flow developed underneath a scaled high-speed train of six coaches featured with both conventional and articulated bogies is investigated based on computational fluid dynamics to establish a contribution to train aerodynamics. The numerical simulations are verified against the experimental measurements. It is found that strong unsteady flow develops around the train, particularly at the regions of nose car, leading bogie, articulated bogies, inter-carriage gaps and tail car, due to flow separations and vortex interactions generated around the geometries. High intensity turbulence appears around the nose, bogies, inter-carriage gaps and tail. Strong vortices and high degree of unsteadiness are produced within the flow between the train underbody and the ground, making the flow developed around the bogie regions of high turbulence. Interaction from the inter-car gap leads to a particularly strong vortical flow around the articulated bogie, causing a large slipstream in the regions close to the airspring and a larger drag. Thus the bogie configuration has a noticeable influence on the train underbody flow.

A Separated-Flow Model for 2-D Viscous Flows around Bluff Bodies Using the Panel Method

Panel methods have been applied to many fields of fluid owing to their computational efficiency. However, their applications are limited in simulating highly turbulent flow with separations due to the inviscid flow assumptions, such as those associated with train aerodynamics. Some researchers employed the wake models to simulate large vortices in the wake of trains with predetermined separation locations according to experimental results. In this paper, a modified 2-D constant source/vortex panel method for modelling the separated flow around 2-D bluff bodies is presented. The proposed separated-flow model includes the prediction of separation locations based on the integral boundary-layer method and the shear layer, and large vortices in the wake of the bluff bodies are modelled by the wake model. The proposed method is validated by comparing the calculated pressure distribution on a 2-D circular cylinder with the experimental results. The method is then applied to simulate the flow around a 2-D generic train and calculate the pressure distribution on the train. Since trains run very close to the ground, the effect of the ground configuration on the pressure distribution of the 2-D train is also investigated in this paper using the proposed method. The main contribution of the work is to present a 2-D separated-flow model with wake modelling and separation prediction. The proposed model can be used in the rapid evaluation of bluff-body aerodynamics.

Correlation tests on train aerodynamics between multiple wind tunnels

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 CMx,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.