Train Slipstream Research Articles

Nonlinear spatiotemporal characteristics of wind–rain flow around the trains passing through the tunnel entrance during rainstorms

Tropical storms present a significant risk to the safety of high-speed trains due to the extreme wind and rainfall they bring. This study employs Eulerian multiphase and Shear-Stress Transport k-ω turbulence models for three-dimensional numerical simulations, focusing on wind–rain interactions involving tunnels, embankments, and trains. The reliability of the numerical analysis method for train slipstream pressure is verified by dynamic model test. Based on the scenario of single train running on the embankment and train intersection at the tunnel portal, the train flow around and wake are analyzed successively with different rainfall intensity. The characteristics of nonlinear wind–rain-train flow field are analyzed from the aspects of velocity field, pressure field and turbulent flow. Finally, the mechanism of the influence of rain on the relative flow field is revealed by the spatiotemporal distribution characteristics of rain phase. With the increase of rainfall intensity, the increase of rain phase distribution on the leeward side of the single train strengthened the backflow on the leeward side of the train. Under the condition of the trains intersecting at the tunnel portal, the relatively closed area between the train and the water film weakened the slipstream effect of the train.

Full scale experimental tests to evaluate the train slipstream in tunnels

The train slipstream, i.e. the air velocity induced by the train, is one of the most important aerodynamic effects connected to railway vehicles because it has a direct impact on the safety of passengers on the platform and track workers along the railway line. In recent years, a lot of studies were performed to understand the development of this phenomenon in open field, and specific EU standards, the EN 14067–4 and the TSI were issued. Instead, only few studies have been carried out to analyse the train slipstream in confined spaces (as tunnels, line sections with acoustic barriers, etc.), even though the first results of these analyses have shown that the confinement of the air causes more severe conditions regarding the speed of the air flow. This work aims at studying, through a full-scale experimental campaign, the effects on the air flow speed caused by the train passage. The effects of different train parameters (i.e. train type and length, etc.) and infrastructure parameters (i.e. geometry variations) were analysed. Lastly, the results of a specific test considering the presence of a stationary train inside the tunnel while another train is passing are described, to simulate scenarios of ordinary railway traffic.

A Numerical Study Toward Harvesting Power From Train Slipstream Using Savonius Rotor

AbstractA novel and strategic green energy production method that utilizes relative wind generated from moving vehicles is presented. A speeding train generates an enormous wake of wind around it, which stocks a substantial amount of kinetic energy. In this study, this freely accessible wind power is harvested by installing a modified savonius wind turbine within the slipstream region of the train. A computer-oriented fluid-solid integrate simulation of wind turbine propelled by train-induced wind is performed by executing all physically realistic boundary conditions. The numerical study is based on open-source CFD toolbox openfoam, and the results were validated against benchmark experimental study. Parametric sensitivity analysis such as optimal turbine performance within the slipstream regime, torque prediction from express trains, two opposite crossing trains, tunnel condition, and turbine wind turbine clusters arrangement has been reported. This study enhances the understanding of the power generation by the turbine from the train slipstream which is not reported in any open literature as far as the authors’ present knowledge goes.

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.

The effect of bogie fairings on the slipstream and wake flow of a high-speed train. An IDDES study

In this study, an improved delayed detached eddy simulation (IDDES) method based on shear-stress transport k-ω turbulence model has been used to investigate the slipstream and wake flow around a high-speed train with different bogie fairings at Re = 1.85 × 106. The accuracy of the numerical method has been validated by wind tunnel experiments and full-scale field tests. Further, the train slipstream, underbody flow and wake structures are compared for three cases. The results show that the bogies covered by full size bogie fairings significantly decrease the train slipstream velocity and weaken the pressure fluctuation around the high-speed train, especially near the bogie regions. Compared to the maximum slipstream velocity at trackside position in Case 2 (half size fairings), it increases by 15.2% in Case 1 (no fairing) and decreases by 16.1% in Case 3 (full size fairings), respectively. The larger size fairings are found to reduce the scale of longitudinal vortices and decrease the streamwise vorticity level in the wake region, thereby lowering the slipstream velocity distribution in the wake. Finally, the larger bogie fairings are recommended to improve the train aerodynamic performance as well as to improve the safety of trackside workers and passengers standing on the platform.

The effect of bogies on high-speed train slipstream and wake

Slipstream, which is the induced air movement generated by a high-speed train (HST) as it passes, is both a safety hazard to commuters and trackside workers, and can cause damage to infrastructure along track lines. Bogies have been shown to exert a strong influence on HST aerodynamics by altering the underbody flow, and their effects have been extensively studied previously from the perspectives of ballast flight and drag reduction. In contrast, the effect of bogies on slipstream characteristics, and especially on the structure of the wake, is less well understood. This study explicitly investigates the effect of bogies on HST slipstream characteristics based on two generic train configurations: a Simplified Train Model (M1) with the bogies covered by a flat surface, and a Full-featured Train Model (M2) with simplified bogie-sets. The bogie effects are revealed through a systematic comparison of flow structures, slipstream characteristics and aerodynamic forces between these configurations. Remarkably, this study discovers that the generation of the strong spanwise oscillation of the wake, observed especially in the presence of bogies, can be interpreted as due to seeding and amplification of a natural instability of the time-mean pair of counter-rotating vortices behind the tail, rather than through direct side-to-side vortex shedding from the bogie geometry. This paper also documents how the altered wake flow affects slipstream characteristics through statistical and gust analyses, and the effect of the bogies on aerodynamic loading by comparing the train surface pressure distributions between the configurations.

The effect of the ground condition on high-speed train slipstream

Understanding the induced movement of air as a high-speed train passes (slipstream) is important for commuter and track-side worker safety. Slipstream is affected by the movement of the train relative to the ground, but this is difficult to include in wind-tunnel tests. Using simulations based on the Improved Delayed Detached Eddy Simulation model, this study investigates the effect of relative ground motion on slipstream for three different ground/wheel configurations: a stationary ground with stationary wheels, a moving ground with stationary wheels, and a moving ground with rotating wheels.By examining the interaction between the train-induced flow structure and ground boundary layer, this study identifies two ways that the ground boundary layer changes slipstream: through directly altering the high slipstream velocity region due to the ground boundary-layer development, and through indirect widening of the wake by deformation of the trailing vortices. The altered aerodynamic loading on a train due to relative ground motion is visualised through the surface pressure distribution, allowing the resultant impact on drag and lift to be assessed. For wheel rotation, it is concluded that its effect is mainly restricted to be within the bogie regions, with limited influence on the wake behind the train.

The performance of different turbulence models (URANS, SAS and DES) for predicting high-speed train slipstream

The air movement induced by a high-speed train (HST) as it passes, the slipstream, is a safety hazard to commuters and trackside workers, and can cause damage to infrastructure along track lines. Because of its importance, many numerical studies have been undertaken to investigate this phenomenon. However, to the authors' knowledge, a systematic comparison of the accuracy of different turbulence models applied to the prediction of slipstream has not yet been conducted. This study investigates and evaluates the performance of three widely used turbulence models: URANS, SAS and DES, to predict the slipstream of a full-featured generic train model, and the results are compared with wind-tunnel experimental data to determine the fidelity of the models. Specifically, this research aims to determine the suitability of different turbulence modelling approaches, involving significantly different computational resources, for modelling different aspects of slipstream.

On the effect of crosswinds on the slipstream of a freight train and associated effects

When a train moves through the air, a region of air moves along with it at approximately the same speed: this region of air is known as the ‘slipstream’. Numerical simulations were conducted in order to simulate the slipstream around a model-scale freight train when subjected to crosswinds with two different yaw angles; 10° and 30°. The results were compared to a previous slipstream study without a crosswind. The velocities on the windward side of the train for each case are mostly lower than the crosswind speed due to the flow stagnation on the side of the train. In general, crosswind velocities are lower than those in the no-crosswind case. On the leeward side, velocities from the 30° crosswind case remain higher than train speed for more than two metres from train side. Peak instantaneous velocities showed strong dependence on yaw angle and position from train side as well as exhibiting superficial comparison to full-scale data. Velocities were used as inputs to a spring-mass-damper model which modelled human responses to wind gusts. The effect of a crosswind on the train's slipstream significantly increased the likelihood of a person becoming unsteadied while standing on the leeward side of the train.

A review of train aerodynamics Part 2 – Applications

AbstractThis paper is the second part of a two-part paper that presents a wide-ranging review of train aerodynamics. Part 1 presented a detailed description of the flow field around the train and identified a number of flow regions. The effect of cross winds and flow confinement was also discussed. Based on this basic understanding, this paper then addresses a number of issues that are of concern in the design and operation of modern trains. These include aerodynamic resistance and energy consumption, aerodynamic loads on trackside structures, the safety of passengers and trackside workers in train slipstreams, the flight of ballast beneath trains, the overturning of trains in high winds and the issues associated with trains passing through tunnels. Brief conclusions are drawn regarding the need to establish a consistent risk based framework for aerodynamic effects.

The Calculation of Train Slipstreams on Platform of Underground High-Speed Rail Station

This paper describes the results of numerical work to determine the flow structures of the slipstream and wake of a high speed train on platforms of underground rail station using three-dimensional compressible Euler equation. The simulations were carried out on a model of a simplified three-coach train and typical cross-section of Chinese high-speed railway tunnel. A number of issues were observed: change process of slipstreams, longitudinal and horizontal distribution characteristics of train wind. Localized velocity peaks were obtained near the nose of the train and in the near wake region. Maximum and minimum velocity values were also noticed near to the nose rear tip. These structures extended for a long distance behind the train in the far wake flow. The slipstream in platform shows the typical three-dimensional characteristics and the velocity is about 4 m/s at 6 m away from the edge of platform.

Full-scale measurement and analysis of train slipstreams and wakes. Part 2 Gust analysis

Part 1 of this paper reports results from the extensive full-scale slipstream measurements carried out as part of the AeroTRAIN project, and in particular concentrates on the ensemble analysis of this data. This paper concentrates on the analysis of maximum gusts, in order to make suggestions for modifications to the current technical specifications for interoperability (TSI) methodology. The very large data set obtained for one particular high-speed train type (the S-103) enabled the variation of slipstream gusts with vehicle speed and wind speed to be determined. It was also possible to carry out a statistical analysis of the gusts that enabled the standard uncertainty of the TSI gust parameter to be determined. It was shown that for most trains the maximum gusts occurred in the near wake of the train, but for double-unit trains the maximum gusts could occur around the gap between the units and for locomotive/coach combinations the maxima could occur around the nose of the locomotive or at the discontinuity between the train and the locomotive. Perhaps the most significant result, which could allow a considerable simplification of the TSI methodology, was that if both trackside and platform measurements for a particular train were plotted against height above the rail, then, with very few exceptions, they fell onto one curve, which implies that a trackside measurement could replace the current required platform measurement.

Full-scale measurement and analysis of train slipstreams and wakes. Part 1: Ensemble averages

This paper describes a series of extensive and unique full-scale measurements of the slipstreams of trains of various types that were carried out as part of the EU-sponsored AeroTRAIN project, together with the analysis of the experimental data. These experiments were carried out with the fundamental aim of seeking to reduce the complexity of the current technical specifications for interoperability (TSI) testing methodology. Experimental sites in Spain and Germany were used, for a range of different train types – high-speed single-unit trains, high-speed double-unit trains, conventional passenger units and locomotive/coach combinations. The data that was obtained was supplemented by other data from previous projects. The analysis primarily involved a study of the ensemble averages of the slipstream velocities, measured both at trackside and above platforms. The differences between the flows around different train types were elucidated, and the effect of platforms on slipstream behaviour described. A brief analysis of the effects of crosswinds on slipstream behaviour was also carried out. Through a detailed analysis of slipstream velocity components, the detailed nature of the flow around the nose and in the near wake of the train was investigated, again revealing differences in flow pattern between different trains. Significant similarity in the far wake flows was revealed. These fundamental results form the basis for the detailed discussion of the proposed TSI methodology that will be presented in Part 2 of this paper. Overall the results enable the nature of the flow field around trains to be understood in far greater detail than before, and also allow the developments of a revised TSI methodology which is more efficient than current practice.

The calculation of train slipstreams using large-eddy simulation

High-speed trains push air to the front, sides and over the top to form a train slipstream. The extension of the slipstream to the side, top and wake flow depends on train speed, train shape, ambient conditions and the environment in which the train operates. In this paper, the slipstream and wake flow of a 1/20th scale model of a simplified five-coach ICE2-shape train running in two different environments; in open air and when passing a platform, were obtained using large-eddy simulation (LES). The flow Reynolds number was taken to be 300,000; based on the speed and height of the train. The effect of the platform height on the train slipstream was investigated by performing simulations on a platform of different heights: 20, 60, 90 cm. To investigate the effect of mesh resolution on the results, two different computations were performed for the case of the flow around the train running in the open air using a different number of mesh nodes; a fine mesh consisting of 18,000,000 nodes and a coarse mesh consisting of 12,000,000 nodes. The results of the coarse mesh simulation were deemed to be comparable to those from the fine mesh simulation. The LES results were also compared with full-scale data and a good agreement obtained. A number of different flow regions were observed in the train slipstream: upstream region, nose region, boundary layer region, inter-carriage gap region, tail region and wake region. Localized velocity peaks were obtained near the nose of the train and in the near wake region. Coherent structures were formed at the nose, roof and inter-carriage gaps of the train. These structures spread in the slipstream and extend a long distance behind the train in the far wake flow. The maximum slipstream turbulent intensity was found in the near wake flow. The results showed that there is a significant effect of the platform height on the slipstream velocity and nose and tail pressure pulses. However, there is only a minor effect of the platform height on the static pressure along the body of the train compared with that on the nose and tail pressure pulses. In general, the slipstream velocity in the lower region of a train running in the open air was found to be larger than that around a train passing a platform. This has been related to the effect of the underbody complexities of the train.

Passenger Train Slipstream Characterization Using a Rotating Rail Rig

This paper presents the results of a new experimental technique to determine the structure of train slipstreams. The highly turbulent, nonstationary nature of the slipstreams make their measurement difficult and time consuming as in order to identify the trends of behavior several passings of the train have to be made. This new technique has been developed in order to minimize considerably the measuring time. It consists of a rotating rail rig to which a 1/50 scale model of a four car high speed train is attached. Flow velocities were measured using two multihole Cobra probes, positioned close to the model sides and top. Tests were carried out at different model speeds, although if the results were suitably normalized, the effect of model speed was not significant. Velocity time histories for each configuration were obtained from ensemble averages of the results of a large number of runs (of the order of 80). From these it was possible to define velocity and turbulence intensity contours along the train, as well as the displacement thickness of the boundary layer, allowing a more detailed analysis of the flow. Also, wavelet analysis was carried out on different runs to reveal details of the unsteady flow structure around the vehicle. It is concluded that, although this methodology introduces some problems, the results obtained with this technique are in good agreement with previous model and full scale measurements.

A study of the slipstreams of high-speed passenger trains and freight trains

As the speeds of both passenger and freight trains increase, there is increasing concern that the unsteady gusts generated in train boundary layers and wakes will become more of for a risk to passengers waiting on platforms and for trackside workers. In addition, the demands of interoperability make this a problem of growing relevance to railway operators across Europe. A number of model scale and full-scale experiments have been carried out in recent years that have provided robust experimental data to quantify these flows. This paper considers all the available datasets for high-speed passenger trains and container freight trains, and in making a comparison between them, arrives at a number of conclusions concerning the characteristics of train slipstreams. It is concluded that the identification of a number of distinct flow regions in earlier work is generally valid and forms a useful framework for the consideration of the problem. The flow characteristics are different in each region, and, depending upon the train type, the measurement distance from the train and height above ground, the observed peak gusts for a train may occur at any time during the train passage or in its wake. It is also concluded that results obtained from measurements around small scale moving models are in good agreement with the full scale measurements and reproduce all the important flow features.