Train Aerodynamics Research Articles

Lateral aerodynamic interference between an interior train and a flat box bridge-deck

This paper studies the crosswind aerodynamics of an interior train and flat box bridge-deck system via a series of wind tunnel experiments in wind angle of attack α = [−12°, 12°]. Aerodynamics of the train- and bridge-only models is measured as benchmarks under similar conditions. Upon comparing with the train- and bridge-only cases, the lateral aerodynamic interference between the train and bridge-deck is qualitatively identified by smoke-wire visualization and quantitatively detected by surface pressure and flow profiles located 8 mm upstream from the train model and 490 mm downstream from the bridge-deck model. Generally, the lateral aerodynamic interference on the train model is primarily manifested by suppression of underbody vortex shedding, shielding effect of bridge-deck leading-edge, and quasi-Reynolds number effect. Compared to the train-only case, the suppression of underbody vortex shedding reduces fluctuating drag, lift, and moment coefficients, whereas the shielding effect decreases the mean drag coefficient. The quasi-Reynolds number effect, owing to the accelerated and turbulent approaching flow over the rounded shoulder of the train model as α varies, abruptly alters drag, lift, and moment coefficients mimicking the classical Reynolds number effect, while the inflow Reynolds number remains unchanged. On the other hand, the lateral aerodynamic interference on the bridge-deck model is chiefly presented as flow transition promoting effect and intensifying effect on bridge-deck trailing-edge flow separating. Compared to the bridge-only case, the flow transition promoting effect leads to the global centerline of the bridge-deck aerodynamics to be parallel shifted about 4° to the positive direction of α, while the intensifying effect increases fluctuating drag, lift, and moment coefficients. Finally, the aerodynamics of the whole train-bridge system is briefly discussed.

The effect of ground clearance on the aerodynamics of a generic high-speed train

The influence of ground clearance on the flow around a simplified high-speed train is investigated in this paper. Four clearance heights are studied using IDDES. After a grid independence study, the results of the simulations are validated against experimental data present in the literature. It is found that the drag decreases when reducing the clearance gap from the baseline height to a possibly critical height, while drag remains constant when the clearance is lower than this critical height. The negative lift (downforce) increases with the decreasing of the clearance gap. The flow is particularly influenced by the gap height at the underbody and wake regions, where a lower underbody velocity and a higher wake velocity are observed with lower clearance down to case h2. Therefore, the different topologies of the wake are presented and described. Particular attention is paid to the description of the wake flow and to the position and the formation of the flow mixing region. Specifically, with decreasing clearance, the mix of the tail downwash and underbody flows happen earlier, and the core of the counter-rotating vortices in the wake tends to develop with an increasing height trend. Overall, aerodynamic performance and flow structure descriptions show positive and negative effects when decreasing gap clearances, which should be taken into account for new design strategies.

Impact monitoring characteristics of piezoelectric paint sensor by thermal fatigue analysis for railroad vehicle applications

The strong aerodynamic drag under a railroad vehicle in motion causes the track ballast to fly up and around. The flying ballast can collide with the underside of the coach, damaging the electronics installed there. There are even cases wherein the aerodynamics of fast-moving train causes the gravel to hit the side of the coach and break the windows. Extensive and numerous studies are underway to reduce the damage caused by such phenomena. In this study, a “smart paint sensor” for impact monitoring was fabricated using piezoelectric nano powder and commercial paint for railroad vehicles, and the application of impact monitoring to railroad vehicles was analyzed. The process was simplified because the use of commercial paint eliminated the need to apply an additional layer of functionalized paint. Furthermore, the fact that the paint can be evenly sprayed on a large surface made it suitable for use on large and intricate objects such as a railroad vehicle bogie. Because railroad vehicles are exposed to thermal stress for a long period of time, a thermal fatigue test was conducted in order to figure out the stability of the polymer-based material, which is relatively vulnerable to temperature variations. The test results were used to analyze the impact sensitivity of the piezoelectric paint sensor. For the analysis, a full-size mock-up of the railroad vehicle bogie and an impact monitoring system with piezoelectric paint sensor were implemented in order to visualize the impact signals from differently shaped objects with large surfaces.

Impact of the trailing edge shape of a downstream dummy vehicle on train aerodynamics subjected to crosswind

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.

The impact of rails on high-speed train slipstream and wake

Slipstream is the induced movement of air as a high-speed train (HST) passes. Previous studies have shown that the development of slipstream is highly geometry dependent, including both the geometries of the trains and nearby objects. Much effort has been channelled into reducing slipstream through optimisation of the train geometry; however, the impact of the rails on train aerodynamics remains largely unexplored. This study analyses the effect of rails on HST slipstream characteristics by systematically comparing the wakes for two geometric configurations incorporating: No Rails (NR) and With Rails (WR). The train model remains identical in both configurations, with the only difference being whether rails are included. This study highlights the potential effects of rails on HST slipstream characteristics, and reveals the underlying mechanism of how the rails shape the wake flow structures. By examining both mean and time-dependent flow features, the simulations show that the rails can significantly alter slipstream characteristics, especially the downstream evolution of the wake, effectively by reducing the lateral movement of the mean streamwise vortex structures, despite the relatively small length scale of the rail cross-section. Perhaps surprisingly, the slipstream measured at the standard distance from the train centerplane, is found be significantly reduced.

Aerodynamic effects of the gap spacing between adjacent vehicles on wind tunnel train models

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%.

Optimal Shape Design of Medium-Speed Train based on Aerodynamics Performance

Train aerodynamic performance greatly affects the efficiency of driving energy and passengers’ comfort. This paper aimed to simulate several forms of train models that produce low and stable aerodynamic obstacles as well as low noise at medium speeds of 120 – 1 50 km/hr. The first step to do was the study of literature on train design models, aeroacoustics, aerodynamics, and human ergonomics. Existing 3D CAD and S-R train models with slender ratios = 4, 6, and 8 were tested using Computational Fluid Dynamics (CFD) and Computational Aerospace (CAA) to determine the impact of airflow. The models that have been built were tested at medium speeds of 120 to 150 km/hr. The final simulation results showed that the existing train produced a drag coefficient (Cd) of around 1.27, average noise of 35.9dB, and fuel requirements by 1.7 liters/km. It is different from trains with a slenderness ratio = 6 that produces the best aerodynamic performance with a drag coefficient (Cd) around 0.436, average noise of 9.4 dB, and fuel consumption of 0.73 liters/km. The results concluded that the medium speed needs to adjust the S-R train model with a slenderness ratio = 6 that can produce an aerodynamic performance to improve train user comfort and save fuel.

Numerical studies on aerodynamics of high-speed railway train subjected to strong crosswind

Under the action of strong crosswind, the aerodynamic behavior of a rail vehicle at high speed will be changed significantly, which could directly affect the safe operation of the vehicle. With the help of the shape of train used in China, the aerodynamic characteristics of trains with scale of 1:1 is investigated using computational fluid dynamics numerical simulation method, which consists of the variation of aerodynamics force and moment with wind yaw angle, wind speed, train speed, and nose shape. After an initial validation against Baker’s results from wind tunnel test, the numerical model is then used to investigate the aerodynamic characteristics of the trains. The numerical results indicate that lift coefficient of the M train is slightly higher than TMC1 and TMC2 trains. Regardless of aerodynamics force coefficients, TMC1 reaches the maximum at a yaw angle of 75°. Aerodynamics force coefficient increases with both wind speed and train speed, but the change of which is not linear. Comparing aerodynamic force with different geometric dimensions of train nose, it is shown that height–width ratio is insensitive to side force and rolling moment, but sensitive to lift force from the yaw angle 0°–90°. The side force coefficient, as we most concern, is less than other results, when the length–width ratio is 1 and height–width is 0.87.

Atmospheric boundary layer modeling in a short wind tunnel

Abstract The aim of the study was to analyze and design through experimental and numerical investigations a passive device to control the development of the boundary layer in an existing short wind tunnel to reproduce conditions representative of an atmospheric boundary layer for wind engineering applications. The current main use of the tunnel being for automotive and train aerodynamics, constrained the design to look for a reversible solution. The approach followed was then to install a grid of horizontal bars of squared cross-section with different dimensions at the entrance of the experimental chamber. The distribution of the bars was selected to be symmetric with respect to the horizontal longitudinal mid-plane of the tunnel. The approach has been validated through experimental measurements by hot-wire anemometry and numerical simulations based on finite volume RANS of the full wind tunnel geometry. The analysis showed that the grid acting as a passive flow control device was effective to reproduce in a short wind tunnel the main characteristics of an atmospheric boundary layer.

Aerodynamics of a scale model of a high-speed train on a streamlined deck in cross winds

The cross wind aerodynamics of a high-speed train (HST) on a streamlined deck was investigated using sectional models in a wind tunnel. Aerodynamics of the HST-only model was also measured as a benchmark under similar conditions. The experimental results indicate that when the HST is on the downstream track of the deck it experiences significant changes in its aerodynamics depending on the angle of attack (α) of the oncoming flow. With an increase in α beyond zero, the mean drag and mean lift forces on HST begin to decrease or increase rapidly. This observation is attributed to the variation in the flow regime around HST from subcritical to critical although the approaching flow Reynolds number (based on the free-stream oncoming flow velocity U∞ and the height of train d) remains unchanged. The separated shear flow from the leading edge of the bridge impinges on the upstream shoulder of the HST on the downstream track at a critical orientation of the approach flow angle. The resulting accelerated flow in the shear layer, characterized by higher turbulence intensity, prompts the flow regime transition near the upstream shoulder of the HST without a change in the inflow Reynolds number. This change in the pressure field over the upstream shoulder of HST when it is on the downstream track on the bridge bears strong similarity to the changes experienced by circular cross-sections or cross-sections with rounded corners with a change in the inflow Reynolds number.

Effect of the outer windshield schemes on aerodynamic characteristics around the car-connecting parts and train aerodynamic performance

Abstract With the increasing speed of passenger trains, the train aerodynamics has deteriorated significantly. Abnormal vibration of windshield of the high-speed train occurred in the test of raising train speed to 350 km/h. To improve the design of a windshield with better aerodynamic performance, the aerodynamic performance of a high-speed train running at a speed of 350 km/h, especially the flow field around the windshields with six configurations, was investigated by numerical simulation and full-scale testing. The results show that the drag of the head car and tail car, and the lift force of the tail car are decreased by the most modified windshields, and the lift force of the head car is increased by the most modified windshields. Fluctuations of the drag and lift force of the tail car are reduced and increased by the modified windshields, respectively, and the effect of modified windshield on the fluctuation of the head car is confused. Vibration of the outer windshield is not suppressed, and even intensified by the modified windshields, and has no obvious relationship with windshield structure.

A full-scale experimental investigation of passenger and freight train aerodynamics

The movement of a train creates a disturbance to the air through which it passes, known as a slipstream. Such disturbances are characterised by changes in pressure, notably around the vehicle nose/tail, and a highly turbulent boundary growth along the vehicle side with an increasing slipstream velocity magnitude. Although these characteristic features occur in some form for all trains, the flow development associated with various train types can often be very different. Variability in train type makes it difficult to accurately characterise the aerodynamic effects of each individual train. In this paper, a detailed set of tests are undertaken to assess the aerodynamic flow development created around various train types common to the UK railway network. A comparison of the analysed data from different passenger and freight trains was made. The variability of freight train results was larger in comparison to the passenger trains examined, because of the large flow separations around the bluff freight train. Although the speed was lower for freight trains, the slipstream velocity and pressure magnitudes were larger than those observed for passenger trains. Passenger trains could be divided aerodynamically into two main types: long distance passenger trains and commuter trains. Longer train lengths were shown to increase the boundary layer growth: an important feature for long distance passenger trains as it creates an increase in the slipstream velocity peak magnitude at the train tail. Boundary layer stabilisation is not observed as in previous studies. The coupling of two carriage sets together, creating a large V-shaped region at the centre of the train, led to a clear step slipstream velocity peak coinciding with the change in pressure at the coupling region. Cross-correlation of results from measuring positions within the characteristic turbulent length scale range appeared to show similar results to autocorrelation time scales for larger scale separation of turbulent structures from the bogie and inter-carriage regions.

Aerodynamics of high-speed maglev trains passing each other in open air

With increasing train speed, aerodynamic effects pose a safety risk for train operations, especially for trains passing each other, the strong transient aerodynamic loads could result in window breakage, sideward shaking, trackside worker injuries, and facility fatigue damage. Unsteady compressible numerical simulation is carried out in this paper to investigate the transient flow field induced by two maglev trains passing each other at a speed of 430 km/h in open air. Good agreement is obtained between the numerical method and full-scale experiment results, with differences smaller than 6%. The transient pressure change on train surfaces and the slipstream distributions on trackside are analysed. It was noted that the peak values of pressure coefficient for two trains passing each other are approximately twice as larger as that of a single train passing because of the blocking effect and interference by the motion of the other train in the opposite direction. The maximum slipstream velocity occurs at a height of 1.4 m from the top of rail (TOR) at the meeting position, and the relationship between the slipstream velocity and the distance from the centre of rail (COR) is obtained, based on which, the safe distance is calculated.

Experimental investigation of the aerodynamics of a freight train passing through a tunnel using a moving model

The objective of this study was to investigate the aerodynamic effects of a freight train passing through a tunnel. The nose entry generates a complex pattern of reflective pressure waves (piston effect) which can lead to intense aerodynamic forces. Previous research on the topic has focused on passenger trains because of higher speeds. The experiments of this study use a 1/25th scaled moving model at the TRAIN Rig at a speed of 33.5 m/s with a blockage ratio of 0.202. The monitored pressure along the tunnel wall can increase up to almost 1000 Pa because of the initial compression wave, while it drops when an expansion wave or the tail passes by. The maximum pressure is observed at the train nose due to air stagnation (1500 Pa) where the flow is steady, while the roof and sides experience negative pressures due to unsteady flow separation. The effect of loading configuration is significant as partially loaded trains can create a second pressure peak on the tunnel walls (after the initial compression wave) and affect the flow at the tunnel entrance wall. Under the current testing conditions, the results indicated compliance with the requirements of the Technical Specification for Interoperability and a constant pressure gradient of the initial compression wave which is in contrast with the passenger train's two-part gradient. Further work on the topic could provide visual information about the exiting jet towards the portal and the separation bubble around the train.

Investigation of High-Speed Train Drag with Towing Tank Experiments and CFD

In order to assess the accuracy of drag prediction methods for high-speed trains, experimental and numerical investigations were performed. Besides the drag coefficient, skin friction and pressure distributions on and near the model have been measured for a 1:22 model of the ICE/V. For the experiments, a moving model rig called DIWA (Drag measurement in water) was realised in a 120 m long towing tank to allow for a realistic simulation of the flow around the train, even in the underbelly region. Numerical investigations were performed using Partially-averaged Navier-Stokes (PANS) simulations based on the k-ω-SST turbulence model. Both experimental and numerical methods can be considered as a novelty in the field of train aerodynamics. The results are compared with data from full-scale tests. It is shown, that the moving model rig DIWA allows for the measurement of drag coefficients of trains with high accuracy. Furthermore, the data acquired using the PANS approach compares well with the experimental data.

Representativeness of geometrical details during wind tunnel tests. Application to train aerodynamics in crosswind conditions

This work aims to highlight the influence of the scale of reproduction of geometric details on models during wind tunnel tests. An application is presented concerning the reproduction of high voltage lines present on the roof of trains. It is shown that the presence of these geometric artefacts deeply modifies the forces and moments measured under cross-wind. It is also shown that the reproduction of geometric details with the scale of the model is not a sufficient condition to ensure a good representativeness of the tests. It is necessary to ensure that the changes in the flow dynamics caused by the presence of the details are correctly reproduced (separation-reattachment process on the roof of the train in this study). The influence of the scale of reproduction of the geometrical details is also studied and a method is proposed to extrapolate the results obtained without roof-lines in order to predict the rolling moment in the presence of roof-lines.

Application of wavestrapping statistical technique to estimate an extreme value in train aerodynamics

This paper explores the application of a statistical analysis technique known as ‘wavestrapping’ to a railway data analysis problem in train aerodynamics. This simulation technique is used to reproduce/reconstruct signals with the same statistical properties of the initial signal(s) and to estimate an extreme value in train aerodynamics. This technique is compared with the method currently used in practice to estimate the peak value of slipstream air speed, according to the European standard EN 14067.

Aerodynamics of Train in Overturn Process under Crosswind

Overturn could happen if train is subjected to strong wind. Numerical simulations were conducted in order to simulate the flow around train when subjected to cross wind with several overturn angles. Non-linear trend of rolling moment was obtained, and the lateral forces and lift have different impact on the moment. The location of maximum positive pressure and minimum velocity moved from side surface to the bottom surface with overturn angle increased. Flow separation velocity is lower at big overturn angle because of the slant surface.

Numerical Simulation of Aerodynamic Drag of Single High-Speed Train Passing through a Tunnel

Train aerodynamics problem must be solved with the development of high-speed railway around the world, and the drag directly affects the maximum running speed of high-speed train. This paper established the numerical calculation model for single train passing through the tunnel with the real configuration of a domestic EMU with eight carriages. The formation mechanism and variation characteristics of the drag over time were analyzed. The drag value and the distribution characteristic of the individual parts were studied at different times of the train passing through the tunnel. The maximum and minimum drag values of the tunnel were compared with the drag of the open air condition. Results indicate the Mach wave directly affected on the pressure drag, the aerodynamic drag distribution of the whole train is changed over time and the fluctuation range of the pressure drag is larger than the friction resistance when the train passing through the tunnel. The maximum value and minimum value of total drag when the train passes through the tunnel are 1.95 times and 0.88 times of that in the open air. When the train is running in the open air, the pressure drag and frictional drag accounted for 61% and 39% respectively of the total aerodynamic drag.

Aerodynamic Characteristics and Safety of High-Speed Trains Embankment under Crosswinds

This paper studies aerodynamic performance and safety of the high-speed train on the embankment under the action of horizontal wind. Based on the aerodynamics and multi-body system dynamics theory, the high-speed train aerodynamics and dynamics model is established to simulate field characteristics, aerodynamic performance and dynamic performance of high-speed train running on 10-meter embankment. From the simulation we get safety indexes such as derailment coefficient, wheel weight reducing load rate, lateral wheelset force and the wheel/rail vertical force. And the running security region of the train on the embankment can be determined based on high-speed train vehicle test specification. The calculation results of this paper can provide reference for the safe operation of high-speed trains in horizontal wind.