Article

On side-wind stability of high-speed trains

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Abstract

In order to achieve maximum performance and cost-efficiency, it is necessary to construct ever lighter trains. As the weight decreases, the impact of the aerodynamic forces increases, particularly for high-speed trains which are exposed to strong cross-wind gusts. Computational Fluid Dynamics (CFD), experimental data and Multi-Body Simulation (MBS) are used to detect the relevant parameters that are responsible for side-wind stability. Although reports of train accidents due to side wind dates back to the 19th century fundamental studies on this issue have been published only in recent years [1]. A detailed sensitivity study of the relevant parameters as aerodynamic axial rolling moment, aerodynamic lift, secondary spring stiffness of the bogie, position of the center of gravity and others will be presented. This sensitivity study shows the achievable side-wind stability of nowadays high-speed train concepts and allows to estimate the potential of improvements for future trains. In order to achieve a substantially higher side-wind stability, it is necessary to improve the aerodynamic performance of the car body in conjunction with an optimisation of the bogie design and shifting the center of gravity of the leading car towards the front.

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... Good overviews are given, for example, in references [1] to [5]. A few studies in the open literature have investigated the influence of crosswind on rail vehicle dynamics [6][7][8][9][10], where most of these studies used aerodynamics based on steady-state conditions. To fulfil standards like the European Technical Specifications for Interoperability (TSI) [11], unsteady crosswind has to be considered. ...
... The overturning risk of a rail vehicle can be defined by different methods. Overviews of different methods are given, for example in references [6] and [16]. A common safety index is the wheel unloading criterion. ...
... A common safety index is the wheel unloading criterion. It is used in several studies and standards, for example see references [6] to [8], [10], [11], and [17]. The vertical wheel-rail force Q on the windward (inner when curving) rail and the static vertical wheel-rail force Q 0 are then compared. ...
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Rail vehicles in everyday operation experience large lateral influences from curves and track imperfections, yielding large suspension deflections and displacements of the carbody relative to the track. Aerodynamic loads caused by crosswind may deteriorate the conditions that can result in vehicle overturning. This study investigates the influence of crosswind on a high-speed rail vehicle negotiating a curve. A multi-body simulation model of a high-speed rail vehicle is subjected to unsteady aerodynamic loads. The vehicle response is studied for different gusts, and variations of some vehicle parameters are performed.
... α = arctan(U Z /|V|), w here V is the speed of trains. The aerodynamic coefficient C χ (α) can be formulated as follows [37][38][39]: ...
... The aerodynamic coefficient   C   can be formulated as follows [37,38,39]: ...
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Affected by strong wind environments, the vibration of trains will significantly intensify, which will severely impact the running quality of trains. To address such challenges, an improved wind load model is proposed in this paper to simulate the shock of strong wind on trains. The proposed model employs the integral approach to calculate the equivalent wind load on trains and applies it to the body of trains during the dynamics simulation process. Eventually, the two-level running quality threshold curve for passenger and freight trains is acquired through the conditional probability density function and the regularized regression model. This achievement covers train speed restrictions for wind speeds ranging from 0~25 m/s, providing a scientific basis for railway departments to adjust train speeds based on real-time wind speeds. It is of utmost importance for ensuring the safe and efficient operation of trains under strong wind conditions.
... The second issue, which was investigated in this study, has not received much attention in previous studies. Many efforts have been made to use multi-body dynamic models to study the characteristic wind curves, which represent critical crosswind speeds, at which the selected derailment criteria reach their limits and vehicle overturning occurs (Orellano and Schober, 2003;Cheli et al., 2006;Xu and Ding, 2006). Typically, quasi-steady approaches are proposed for use in calculating the wheel loading reduction caused by crosswind forces. ...
... The terms cy, cz, cmx, cmy, and cmz correspond to the aerodynamic force coefficients, which depend on the crosswind attack angle β. The aerodynamic coefficients of the Inter City Express 2 (ICE2) driving trailer (Orellano and Schober, 2003) were used in the calculation of the crosswind forces, as shown in Fig. 5. ...
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A coupled vehicle-track dynamic model is put forward for use in investigating the safety effects of crosswinds on the operation of a high-speed railway vehicle. In this model, the vehicle is modeled as a nonlinear multi-body system, and the ballasted track is mod-eled as a three-layer discrete elastic support system. The steady aerodynamic forces caused by crosswinds are modeled as ramp-shaped external forces being exerted on the vehicle body. This model was used in a numerical analysis of the dynamic re-sponse and dynamic derailment mechanisms of high-speed vehicles subjected to strong crosswinds. The effects of the crosswind speeds, crosswind attack angle, and vehicle speed on the operational safety of the vehicle were examined. The operational safety boundaries of a high-speed vehicle subjected to crosswinds were determined. The numerical results obtained indicate that cross-winds at attack angles of 75° to 90° with respect to the forward direction of the vehicle have a great influence on the safety of oper-ating high-speed railway vehicles. The wheelset unloading limit, which determines the position of the warning boundary dividing the safe operating area and the warning area, is the most conservative, i.e., the safest, criterion to use in assessing the high-speed operational safety of vehicles in crosswinds.
... where ρ is the air density, V is the vehicle speed, U is the wind velocity, c y , c z , c mx , c my and c mz are the aerodynamic force coefficients, which are the function of yaw angle. Aerodynamic coefficients of an ICE2 driving trailer [12] are used in the calculation of wind forces, as shown in Fig. 5. ...
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A coupled vehicle-track dynamic mode is put forward to investigate the effect of crosswind on high speed railway vehicle running safety. The model considers the track motion respect with to the vehicle running on it, therefore characterizes the effect of the rail support by the periodical discrete sleepers on the vehicle/track interaction. The steady aerodynamic forces caused by crosswind are modeled as the ramp shape external forces exert on the car body. The numerical analysis investigates the effects of the crosswind speed and the vehicle speed on the dynamic behavior of the vehicle/track in detail. Then, the vehicle overturning criteria and the wheel rise with respect to the rail are calculated and used to assess the railway vehicle running safety. The numerical results obtained indicate that the crosswind has a great influence on the whole vehicle running safety when the vehicle is just entering the steady crosswind scenario.
... In particular, the running safety is strongly affected by crosswind through the interaction of the centrifugal force and the gravitational restoring force by cant when vehicles run on curved track. Regarding the analysis on overturn caused by a crosswind, several studies [1][2][3][4][5][6][7] have been published, whereas there have been few studies on derailment by a crosswind. ...
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... For yaw angles larger than approximately 40 • , these vortices can become unstable and exhibit a transient behavior. Instability leads eventually to a vortex breakdown for yaw angles exceeding 50 • and for smaller angles the flow basically stays attached [1]. ...
Chapter
In the design process of trains wind tunnel tests are indispensable in order to assess the cross-wind sensitivity. The aerodynamic forces and moments acting on the leading cars or trailer cars can be measured and aerodynamic coefficients determined. Usually the tests are carried out at low turbulence conditions (“smooth flow”). During recent wind tunnel tests on new high speed train models in the Hermann-Föttinger Institute Berlin undesired Reynolds number effects were observed. This paper describes an approach to reduce these effects by changing the turbulence conditions of the flow. Wind tunnel measurement on a high speed train model in scale 1:25 are carried out with different turbulence conditions: increased free stream turbulence and a tripped boundary layer on the model. The free stream turbulence level is varied from 0.5 to 8 % by using grids with different geometries up stream of the test section. The experiments showed that the Reynolds number dependency on the saftey relevant rolling moment can be well reduced by a simple rectangular grid installed in the contraction of the wind tunnel.
... In particular, the running safety is strongly affected by crosswind through the interaction of the centrifugal force and the gravitational restoring force by cant when vehicles run on curved track. Regarding the analysis on overturn caused by a crosswind, several studies [1][2][3][4][5][6][7] have been published, whereas there have been few studies on derailment by a crosswind. ...
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Due to the lightening of railway vehicles and the improvement of operation speeds, the reduction of running safety by cross winds is becoming an important problem. In particular, the running safety tends to reduce when the vehicles are running on curved sections. When a cross wind acts on the vehicle running on a curve from the outer side, a flange climbing phenomenon can occur. In this study, a full vehicle model was constructed using a multi-body software, SIMPACK, and the running simulation on a curve was carried out to examine the running safety under the condition that a cross wind acted on the vehicle from the outer side of the curve. As a result, it is verified that the derailment coefficient of the first wheelset becomes large in the exit transition curve and that of the third wheelset does in the entrance transition curve and this trend is pronounced by larger wind forces. Here, the derailment coefficients at the timing the derailment occurs are different between the first and third wheelsets, and those derailment coefficients are much larger than the critical derailment coefficients obtained by Nadal's formula. Then an equivalent friction coefficient which depends on an attack angle is introduced in Nadal's formula. Consequently, the critical derailment coefficient considering the equivalent friction coefficient came close to the actual derailment coefficient.
... figure 3) shows 3 regions that depend on the skewing angle. Orellano et al. [2] showed, that for modern high speed trains the wheel unloading due to cross wind is strongest for yaw angles of 10 o to 30 o . Due due to the large velocity of the train (v train ≈ 100m/s) relative to the ground, this corresponds to nearly perpendicular wind relative to the track (80 o to 90 o ) with a wind speed of approximately 30 m/s. ...
... In particular, the running safety is strongly affected by crosswind through the interaction of the centrifugal force and the gravitational restoring force by cant when vehicles run on curved track. Regarding the analysis on overturn caused by a crosswind, several studies [1][2][3][4][5][6][7] have been published, whereas there have been few studies on derailment by a crosswind. ...
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Owing to the lightening of railway vehicles and increased operation speeds, the reduction of running safety in the pres-ence of crosswind is becoming an important problem. In particular, the running safety tends to decrease when vehicles run on curved track. When a crosswind acts on a vehicle negotiating a curve from the outer side, flange climbing can occur. In this study, a full-vehicle model was constructed using the multi-body simulation software SIMPACK, and a simulation of a bogie vehicle with two-axle trucks negotiating a curve was carried out to examine the running safety under the condition where a crosswind acts on the vehicle from the outer side of the curve. As a result, it was verified that the derailment coefficient of the first wheelset becomes large in the exit transition curve and the coefficient of the third wheelset does in the entrance transition curve, and this trend becomes pronounced at low operation speeds in the presence of a stronger crosswind. It was also shown that the critical derailment coefficients obtained by modified Nadal's formula considering the effect of attack angle become close to the actual derailment coefficients at the timing that flange climbing occurs.
... The existed research mainly concentrated on the identification of aerodynamic parameters of bridges from the wind tunnel test or in-site measurement (Han et al. 2010, Nikitas et al. 2011, and the wind-induced vibration analysis of large span bridges, including the buffeting, flutter, vortex-excited vibration and wind-rain vibration of bridges (Xiang et al. 2005, Zhang 2011, the train-bridge coupling vibration (Li and Zhu 2010) and the aerodynamic properties and running safety of trains in strong wind field (Li et al. 2005). There have been many research results on wind-induced instability of vehicles on roads without wind barriers (Wetzel et al. 2008, Orellano et al. 2002, Diedrichs et al. 2007, Cooper et al. 1979, Carrarini 2007, Andersson et al. 2004) and on the aerodynamic characteristic of different vehicles on embankments or bridges under cross winds adopting numerical simulation and wind tunnel test method (Ahmed et al. 1985, Cheli et al. 2003, Cooper 1981, Howell 1986, Suzuki et al. 2003. Some efforts were also made to improve the protection, as the vehicles are extremely exposed to strong wind gusts (Baker et al. 1992, Saito et al. 2006. ...
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An analysis framework for vehicle-bridge dynamic interaction system under turbulent wind is proposed based on the relevant theory of wind engineering and dynamics. Considering the fluctuating properties of wind field, the stochastic wind velocity time history is simulated by the Auto-Regressive method in terms of power spectral density function of wind field. The bridge is represented by three-dimensional finite element model and the vehicle by a multi-rigid-body system connected by springs and dashpots. The detailed calculation formulas of unsteady aerodynamic forces on bridge and vehicle are derived. In addition, the form selection of wind barriers, which are applied as the windbreak measures of newly-built railways in northwest China, is studied based on the suggested evaluation index, and the suitable values about height and porosity rate of wind barriers are studied. By taking a multi-span simply-supported box-girder bridge as a case study, the dynamic response of the bridge and the running safety indices of the train traveling on the bridge with and without wind barriers are calculated. The limit values of train speed with respect to different wind velocities are proposed according to the allowance values in the design code.
... From a mechanical point of view, the roll moment and the lift force -in addition to the side force and pitch moment -are the most crucial aerodynamic loads [8]. As regards these aerodynamic loads, the yaw angle has a dominant influence. ...
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This paper presents first results of a joint experimental and computational investigation into the prediction of the cross-wind stability of high-speed trains (HST). Attention is confined to the aerodynamic loads on the first car of a generic HST when exposed to a range of yaw angles (0°
... Orellano et al. [10] showed, that for modern high speed trains the wheel unloading due to cross wind is strongest for yaw angles of 10 o to 30 o . Due to the large velocity of the train a) b) Figure 7: The flow around a swept backward facing step [8] (v train ≈ 100m/s) relative to the ground, this corresponds to nearly perpendicular wind relatively to the track (80 o to 90 o ) at a wind speed of approximately 30 m/s. ...
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An ICE 3 model has been investigated in an automotive wind tunnel on three different ground configurations by means of force measurements and tuft flow visualisations. The aerodynamic force and moment coefficients reveal a strong dependency on the ground configuration, with the embankment configuration giving the highest measured coefficients only for yaw angles β40∘. The coefficients obtained through the Baker hypothesis are found to be larger than those measured directly on the embankment. The poor agreement between the “measured on embankment coefficients” and the “flat ground with Baker transformation coefficients” is attributed to the fundamental mismatch of relative flow velocities between wind, train and ground during the wind tunnel measurements with the train situated on the embankment. The mismatch of flow velocities causes a strong longitudinal vortex on the leeward side of the embankment which does not exist in reality and significantly alters the overall flow field.It is thus recommended, for the determination of aerodynamic forces acting on a train on an embankment, to measure the aerodynamic coefficients for the flat ground configuration and subsequently apply the Baker hypothesis.
Chapter
A coupled vehicle–track dynamic model is put forward for use in investigating the safety effects of crosswinds on the operation of a high-speed railway vehicle. In this model, the vehicle is modeled as a nonlinear multi-body system, and the ballasted track is modeled as a three-layer discrete elastic support system. The steady aerodynamic forces caused by crosswinds are modeled as ramp-shaped external forces being exerted on the vehicle body. This model was used in a numerical analysis of the dynamic response and dynamic derailment mechanisms of high-speed vehicles subjected to strong crosswinds. The effects of the crosswind speeds, crosswind attack angle, and vehicle speed on the operational safety of the vehicle were examined. The operational safety boundaries of a high-speed vehicle subjected to crosswinds were determined. The numerical results obtained indicate that crosswinds at attack angles of 75°–90° with respect to the forward direction of the vehicle have a great influence on the safety of operating high-speed railway vehicles. The wheelset unloading limit, which determines the position of the warning boundary dividing the safe operating area and the warning area, is the most conservative, i.e., the safest, criterion to use in assessing the high-speed operational safety of vehicles in crosswinds.
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The development of free shear layers formed by the mixing of initially separated free streams is examined in a review of recent work. The mixing layer is viewed as a prototype for a class of inviscidly unstable free shear flows including jets and wakes, and the focus is on 2D homogeneous incompressible mixing layers. Major areas covered include dynamical processes in free shear layers, the influence of operational parameters, sensitivity to artificial excitations, and global feedback effects. Graphs, drawings, and photographs of characteristic phenomena are provided.
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An experimental study was made of the effect of a periodic velocity perturbation on the separation bubble downstream of the sharp-edged blunt face of a circular cylinder aligned coaxially with the free stream. Velocity fluctuations were produced with an acoustic driver located within the cylinder and a small circumferential gap located immediately downstream of the fixed separation line to allow communication with the external flow. The flow could be considerably modified when forced at frequencies lower than the initial Kelvin-Helmholtz frequencies of the free shear layer, and with associated vortex wavelengths comparable to the bubble height. Reattachment length, bubble height, pressure at separation, and average pressure on the face were all reduced. The effects on the large-scale structures were studied using flow photographs obtained by the smoke-wire technique. The forcing increased the entrainment near the leading edge. It was concluded that the final vortex of the shear layer before reattachment is an important element of the flow structure. There are two different instabilities involved: the Kelvin-Helmholtz instability of the free shear layer and the ‘shedding’-type instability of the entire bubble. The former consists of an interaction of the shear layer vorticity with itself, the latter with its images that result because of the presence of a wall. In order to determine the optimum forcing frequency, a method of frequency scaling is proposed which correlates data for a variety of bubbles and supports an analogy with Kármán vortex shedding.
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A three-dimensional source/vortex panel method has been developed to predict the aerodynamic loads on an idealized railway train model in a cross-wind at large yaw angles up to 90°. In this model, the surface of the train and the wake on the leeside are modelled by a number of source and vortex panels, respectively. The algorithm involves the combination of a two- and a three-dimensional procedure in which the two-dimensional calculation simplifies dramatically the computation required for the three-dimensional calculation. The results compare well with experiment.