Train In Crosswind 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.

Investigating embedded data distribution strategy on reconstruction accuracy of flow field around the crosswind-affected train based on physics-informed neural networks

PurposePhysics-informed neural networks (PINNs) have become a new tendency in flow simulation, because of their self-advantage of integrating both physical and monitored information of fields in solving the Navier–Stokes equation and its variants. In view of the strengths of PINN, this study aims to investigate the impact of spatially embedded data distribution on the flow field results around the train in the crosswind environment reconstructed by PINN.Design/methodology/approachPINN can integrate data residuals with physical residuals into the loss function to train its parameters, allowing it to approximate the solution of the governing equations. In addition, with the aid of labelled training data, PINN can also incorporate the real site information of the flow field in model training. In light of this, the PINN model is adopted to reconstruct a two-dimensional time-averaged flow field around a train under crosswinds in the spatial domain with the aid of sparse flow field data, and the prediction results are compared with the reference results obtained from numerical modelling.FindingsThe prediction results from PINN results demonstrated a low discrepancy with those obtained from numerical simulations. The results of this study indicate that a threshold of the spatial embedded data density exists, in both the near wall and far wall areas on the train’s leeward side, as well as the near train surface area. In other words, a negative effect on the PINN reconstruction accuracy will emerge if the spatial embedded data density exceeds or slips below the threshold. Also, the optimum arrangement of the spatial embedded data in reconstructing the flow field of the train in crosswinds is obtained in this work.Originality/valueIn this work, a strategy of reconstructing the time-averaged flow field of the train under crosswind conditions is proposed based on the physics-informed data-driven method, which enhances the scope of neural network applications. In addition, for the flow field reconstruction, the effect of spatial embedded data arrangement in PINN is compared to improve its accuracy.

Discrete integration for measuring aerodynamic loads on trains in crosswinds − realizable strategies of discretization and discrete integration

Discrete integration occupies an important place in train aerodynamic tests in crosswinds. Improved delayed detached eddy simulations based on shear stress transport k-ω turbulence models were carried out to calculate the side force, lift, rolling moment around the lee rail, and surface pressure on bluff and streamlined vehicles. The changepoints and piecewise linearities of the pressure coefficients were evaluated, and the maximum coefficient of determination in the elements was 0.9973. A realizable strategy of the discretization based on the Lagrange rectangular elements was suggested, including the largest lengths and numbers of the elements. From this, a strategy of the discrete integration was presented to measure the aerodynamic loads, considering the real orientation of the elements. The maximum errors of the mean aerodynamic load coefficients of the bluff and streamlined vehicles were 4.1% and 2.2% (except the mean lift coefficient of the bluff vehicle), respectively. The errors were less than those in the previous studies, especially for the streamlined vehicle, which reduced by up to 8.7%. The unsteady aerodynamic loads with no delay obtained by the strategies were near to natural ones in the frequency range that people would be concerned about in crosswinds (at the Strouhal number of less than 0.4). Some suggestions were made for using the strategies in the full-scale tests and model tests, which provided a foundation for further studies of the running safety in natural crosswinds.

Dynamic Interaction Analysis and Running Safety Assessment of the Wind–Train–Bridge System Considering the Moving Train’s Aerodynamic Coupling with Crosswind

Trains tend to be faster and lighter to meet the increasing public travel needs and interact with crosswind to produce a strong aerodynamic interaction, leaving a safety hazard for the operation. This paper presents a study into the dynamic response and running safety of the train–bridge system accounting for this aerodynamic interaction. The threedimensional flow features of a moving train in crosswinds are first investigated by a computational fluid dynamics method, and then an aerodynamic model for simulating unsteady crosswind force is developed. Furthermore, the dynamic responses of the train and bridge are calculated by using a wind–train–bridge dynamic interaction equation, and finally, the characteristic wind curve and surface are defined to evaluate the train’s running safety. The results show that the lateral response of the train–bridge system significantly increases as the crosswind increases, and the head car can experience a high derailment risk and determine the running safety of the train due to the aerodynamic coupling effect of a moving train and crosswind. Variations in the wind direction need to be factored into the safety assessment for low train speeds, and the train is at greater danger when the crosswind appears perpendicular to the car body.

CFD Study of High-Speed Train in Crosswinds for Large Yaw Angles with RANS-Based Turbulence Models including GEKO Tuning Approach

Crosswind action on a train poses a risk of vehicle overturning or derailment. To assess if new train designs fulfill the safety requirements, computational fluid dynamics is commonly used. This article presents a comprehensive wind flow analysis on an example of a TGV high-speed train. Large yaw angle range is studied with the application of widely used Reynolds-averaged Navier–Stokes (RANS) turbulence models. The predictive performance of popular RANS-based models in that regime has not been reported extensively before. The context of simulations is a study of crosswind stability using methodology presented in norm EN 14067-6:2018. It is shown that for yaw angles up to 45 degrees, aerodynamic forces predicted by all the studied RANS-based models are consistent with experimental data. At larger yaw angles, flow structure becomes complicated, separation lines are no longer defined by geometry, and significant discrepancies between turbulence models appear, with relative differences between models up to 30%. A detailed study was performed to investigate differences between turbulence models for specific angles of 40, 60, and 80 degrees, which correspond to distinctive ranges of moment characteristics. Finally, a successful attempt was made to tune a GEKO turbulence model to fit the experimental data. This allowed us to reduce the maximum relative error in comparison to the experiment in the full yaw angles range down to 12.7%, which is in line with the norm requirements.

Full-scale tests of unsteady aerodynamic loads and pressure distribution on fast trains in crosswinds

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

Aerodynamics of a two-dimensional bluff body with the cross-section of a train

Experiments on the aerodynamics of a two-dimensional bluff body simplified from a China high-speed train in crosswinds were carried out in a wind tunnel. Effects of wind angle of attack α varying in [−20°, 20°] were investigated at a moderate Reynolds number Re = 9.35 × 104 (based on the height of the model). Four typical behaviors of aerodynamics were identified. These behaviors are attributed to the flow structure around the upper and lower halves of the model changing from full to intermittent reattachment, and to full separation with a variation in α. An alternate transition phenomenon, characterized by an alteration between large- and small-amplitude aerodynamic fluctuations, was detected. The frequency of this alteration is about 1/10 of the predominant vortex shedding. In the intervals of the large-amplitude behavior, aerodynamic forces fluctuate periodically with a strong span-wise coherence, which are caused by the anti-symmetric vortex shedding along the stream-wise direction. On the contrary, the aerodynamic forces fluctuating at small amplitudes correspond to a weak span-wise coherence, which are ascribed to the symmetric vortex shedding from the upper and lower halves of the model. Generally, the mean amplitude of the large-amplitude mode is 3 times larger than that of the small one. Finally, the effects of Reynolds number were examined within Re = [9.35 × 104, 2.49 × 105]. Strong Reynolds number dependence was observed on the model with two rounded upper corners.

The effect of numerical divergence schemes on the flow around trains

The influence of divergence schemes in typical turbulence modelling on the aerodynamic behaviours was investigated in this study. Four common divergence schemes have been used to predict the aerodynamic behaviours of a typical train in crosswinds, including the first order upwind differencing (UD), second order limited-linear differencing (LL), linear-upwind differencing (LU) and Linear-upwind stabilized transport (LUST) schemes. Shear Stress Transport (SST) k–ω turbulence model and Improved Delayed Detached Eddy Simulation (IDDES) were applied to simulate the aerodynamic characteristics of the train. Both SST and IDDES with the above three kinds of the second order divergence schemes are capable of predict accurately the pressure coefficient. Results obtained using SST with the second order discretisation schemes gave similar streamline trends around the train nose and as anticipated, results from the first order UD scheme showed poor comparison. Results obtained using IDDES showed sensitivity to the divergence schemes, and different schemes performing differently in predicting the surface pressure on different parts of the car body. Considerable differences in the force coefficient using IDDES were observed between the LUST and the other schemes. The second order upwind LU scheme is not recommended for IDDES of the flow around trains.

Effect of RANS Model on the Aerodynamic Characteristics of a Train in Crosswinds Using DDES

Detached eddy simulation has been widely applied to simulate the flow around trains in recent years. The Reynolds-averaged Navier-Stokes (RANS) model for delayed detached eddy simulation (DDES) is an essential user input. The effect of the RANS model for DDES on the aerodynamic characteristics of a train in crosswinds is investigated in this study. Three different DDES models are used, based on the Spalart-Allmaras model (SA), the realizable k-ε model (RKE), and the shear stress transport k-ω model (SST). Results show that all DDES models can give relatively accurate predictions of pressure coefficient on almost all surfaces. There are only some specific differences in the small vortices, while similar flow patterns around trains could be predicted. The SST based DDES model (SSTDDES) gives the most accurate numerical results among the three models for the surface pressure. The variations in pressure on the leeward face play a key role in the variation of the side force.

Effect of RANS Turbulence Model on Aerodynamic Behavior of Trains in Crosswind

The numerical simulation based on Reynolds time-averaged equation is one of the approved methods to evaluate the aerodynamic performance of trains in crosswind. However, there are several turbulence models, trains may present different aerodynamic performances in crosswind using different turbulence models. In order to select the most suitable turbulence model, the inter-city express 2 (ICE2) model is chosen as a research object, 6 different turbulence models are used to simulate the flow characteristics, surface pressure and aerodynamic forces of the train in crosswind, respectively. 6 turbulence models are the standard k-ε, Renormalization Group (RNG) k-ε, Realizable k-ε, Shear Stress Transport (SST) k-ω, standard k-ω and Spalart–Allmaras (SPA), respectively. The numerical results and the wind tunnel experimental data are compared. The results show that the most accurate model for predicting the surface pressure of the train is SST k-ω, followed by Realizable k-ε. Compared with the experimental result, the error of the side force coefficient obtained by SST k-ω and Realizable k-ε turbulence model is less than 1 %. The most accurate prediction for the lift force coefficient is achieved by SST k-ω, followed by RNG k-ε. By comparing 6 different turbulence models, the SST k-ω model is most suitable for the numerical simulation of the aerodynamic behavior of trains in crosswind.

On the Reynolds-Averaged Navier-Stokes Modelling of the Flow around a Simplified Train in Crosswinds

On the Reynolds-Averaged Navier-Stokes Modelling of the Flow around a Simplified Train in Crosswinds

A Cylindrical Vehicle-Mounted Anemometer Based on 12 Pressure Sensors—Principle, Prototype Design, and Validation

Vehicle wind speed measurement has always been a vital issue when assessing the aerodynamic performance of a high-speed train in cross winds. Conventional anemometers are not applicable in the extreme environment caused by trains. In this paper, a new wind speed measurement method is proposed, and a cylindrical anemometer to simultaneously measure the wind speed and direction is presented. The instrument consists of a cylinder with 12 evenly distributed holes that connect to 12 differential pressure sensors. Thus, the pressure distribution developed by the wind on the lateral surface of the cylinder is obtained. Then, theoretical relations among three neighboring pressure maxima and the wind speed and wind direction are formulated and validated with a wind tunnel test, where the fabricated anemometer is rotated at 10° intervals under a wind speed of 5–60 m/s. Field tests are conducted to assess the environmental adaptability of the proposed anemometer. The experimental results show that the proposed method and developed anemometer can be applied for air flow measurements and have high accuracy, reliability, and durability.

Trains in crosswinds – Comparison of full-scale on-train measurements, physical model tests and CFD calculations

In this paper a major series of experiments is described that included extensive full-scale measurements of cross wind induced pressures on the Class 43 New Measurement Train over an extended 21 month period, together with wind tunnel, moving model tests and CFD calculations, and allows, for the first time, a proper evaluation of the adequacy of these techniques. Static wind tunnel tests and moving model tests show good agreement with each other, both in terms of the measured pressure field around the train and in the overall side force per unit length over the yaw angle range from 15 to 30°. Similarly the wind tunnel tests and the CFD calculations show good agreement with each other for yaw angles up to 15°. Two different analyses of the full-scale data were carried out - an analysis of 1 s average wind speeds and forces, and an analysis of specific gusts. There was a very great deal of scatter in the results and only the results from simple track topographies were found to agree well with the model and computational results.

Numerical simulation of a regional train in cross-wind

In this work numerical investigations of regional trains were carried out studying the prediction accuracy of the aerodynamic load in cross-wind assessment of rail vehicles. The main focus is on 30° yaw angle. Two domain setups, one representing the wind tunnel setup and another more generic one, were investigated and validated against available measurements comparing load coefficients. Important aspects of a guideline assessing aerodynamic load coefficients with numerical simulation techniques are proposed. Based on practical considerations and on the presented results the use of a generic domain is suggested for virtual certification. Further improvement of the flow field prediction can be achieved using unsteady hybrid numerical techniques, such as detached eddy simulation. Load coefficient results of various unsteady approaches and comparisons of simulated and measured flow fields are shown. Hints about the usage of the employed hybrid method are given, and future investigations are proposed.

Effect of noise barrier on aerodynamic performance of high-speed train in crosswind

A three-dimensional aerodynamic model and a vehicle dynamics model are established to investigate the effect of noise barrier on the dynamic performance of a high-speed train running on an embankment in crosswind in this paper. Based on the developed model, flow structures around the train with and without noise barrier are compared. Effect of the noise barrier height on the train dynamic performance is studied. Then, comparisons between the dynamic performance indexes of the train running on the windward track and on the leeward track are made. The calculated results show that the noise barrier has significant effects on the structure of the flow field around the train in crosswind and thus on the dynamic performance of the high-speed train. The dynamic performance of the train on the windward track is better than that on the leeward track. In addition, various heights of the noise barrier will have different effects on the train dynamic performance. The dynamic performance indexes keep decreasing with the increase of the noise barrier height before the height reaches a certain value, while these indexes have an inverse trend when the height is above this value. These results suggest that optimization on the noise barrier height is possible and demonstrate that the designed noise barrier height of the existing China Railway High-speed line analysed in this article is reasonable from the view point of the flow field structure and train dynamic performance although the noise barrier is always designed based on the noise-related standard.

Dynamics of high-speed train in crosswinds based on an air-train-track interaction model

A numerical model for analyzing airtraintrack interaction is proposed to investigate the dynamic behavior of a high-speed train running on a track in crosswinds. The model is composed of a traintrack interaction model and a trainair interaction model. The traintrack interaction model is built on the basis of the vehicletrack coupled dynamics theory. The trainair interaction model is developed based on the train aerodynamics, in which the Arbitrary LagrangianEulerian (ALE) method is employed to deal with the dynamic boundary between the train and the air. Based on the airtraintrack model, characteristics of flow structure around a high-speed train are described and the dynamic behavior of the high-speed train running on track in crosswinds is investigated. Results show that the dynamic indices of the head car are larger than those of other cars in crosswinds. From the viewpoint of dynamic safety evaluation, the running safety of the train in crosswinds is basically controlled by the head car. Compared with the generally used assessment indices of running safety such as the derailment coefficient and the wheel-load reduction ratio, the overturning coefficient will overestimate the running safety of a train on a track under crosswind condition. It is suggested to use the wheel-load reduction ratio and the lateral wheelrail force as the dominant safety assessment indices when high-speed trains run in crosswinds.

Investigation of train safety domain in cross wind in respect of attitude change

High-speed trains require a lighter weight for speeding up and saving energy; a higher-speed and lighter weight will lead to larger attitude changes for a train travelling in a cross wind, which will threaten its running safety more. This paper presents a new methodology for the assessment on limit safety conditions of High-speed trains subjected to cross wind action while considering the attitude change. The method of defining the stable attitude of a train in cross winds by analysis of fluid-solid coupling vibration is presented. The influence of attitude changes on flow field, aerodynamic loads and running safety of trains is analyzed. The dangerous states and running safeties of a train are analyzed. The safety domain of the train running in cross wind in consideration of the attitude change is defined according to the critical speed of the cross winds of the train running at different speeds. The running safety domain of the train decreases because of changes of aerodynamic loads caused by attitude change. The effect of attitude change on running safety becomes more and more apparent with an increase of train speed and cross wind. Attitude change effects need to be taken into account when calculating aerodynamic loads and the running safety of train.

Equilibrium Characteristics of High-Speed Train in Crosswind

A fast approach to high-speed train co-simulation between aerodynamics and train-track coupling dynamics is presented. With this method, the fluid-structure dynamic performances of a high-speed train are simulated with different crosswind velocity and train velocity. The aerodynamic forces and train dynamics are compared under off-line simulation and equilibrium state method. Considering the fluid-structure interaction, there is significant influence on the head aerodynamics and train dynamics. The results show that it is necessary to consider changing attitude in crosswind

Aerodynamic Forces on Multiple Unit Trains in Cross Winds

This paper describes the results of wind tunnel tests that were carried out to measure the aerodynamic characteristics of an electrical multiple unit (EMU) vehicle in a cross wind. The measurements were made on a 1/30 scale model of the Class 365 EMU in a simulation of the natural wind. The time histories of surface pressures were measured at a large number of points over the vehicle from which the aerodynamic characteristics and force coefficients were determined. This paper describes the complex fluctuating pressure field over the vehicle, through a consideration of the mean and fluctuating pressure coefficients and their spectra, and through a proper orthogonal decomposition analysis, which identifies the major modes of this distribution. The mean, fluctuating, and extreme aerodynamic side and lift forces are also discussed. It is shown that the flow pattern around the vehicle is dominated by large windward roof corner pressure fluctuations.