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This paper studies the aerodynamic characteristics of high-speed trains (HSTs) featuring aerodynamic braking plates installed on the streamlined sections, employing the improved delayed detached eddy simulation (IDDES) method at Re = 5.0 × 105. The precision of the numerical simulation methodology has been validated through reduced-scale wind tunnel experiments. A comparative analysis has been conducted on the characteristics of slipstream, wake flow, and upper flow between the original configuration (OC) and the braking configuration (BC) of the HSTs. The findings reveal that the application of braking plates promotes significant separation phenomena around the HSTs, enhancing the slipstream velocity distribution. In the BC, compared to the OC, the maximum value of the time-averaged slipstream velocity has increased by approximately 134.9% and 76.8% at the trackside and platform positions, respectively. Additionally, the TSI value of the slipstream velocity shows increases of around 100.4% and 210.4% at the trackside and platform positions, respectively. Meanwhile, the turbulence fluctuations within the wake region have been enhanced, with the formation of a longitudinal vortex alongside the railway subgrade, whose core nearly covers the TSI positions. Notably, obvious shifts occur within the upper flow field, which significantly strengthens both flow turbulence and slipstream velocity, potentially influencing components on the upper surface of HSTs, such as the pantograph. The deployment of braking plates contributes to a significant increase in overall vehicle pressure drag, thereby enhancing the train's aerodynamic drag. Relative to the OC, the aerodynamic drag of the HST has increased by approximately 235.4% in the BC. [ABSTRACT FROM AUTHOR]

• A novel load-bearing underframe energy absorption structure for subway trains is proposed. • The crashworthiness characteristics of the aluminum alloy and stainless steel energy absorption component, (i.e., thin-walled tube) is analyzed. • The parameter study of the aluminum alloy thin-walled tube on load-bearing underframe is conducted and the results of the optimized structure is compared with the traditional stainless steel thin-walled tube on load-bearing underframe. • An impact test is conducted to verify the crashworthiness of the optimized load-bearing underframe and the result shows that the proposed energy absorption structure can be utilized on the subway trains. The load-bearing underframe is widely utilized on the crashworthiness design of subway trains. However, studies on load-bearing underframes mainly focused on conceptual design and structural optimization, and didn't consider the combination of bearing loads during the normal operation and absorbing impact kinetic energy under collisions. In addition, the traditional load-bearing underframe for subway trains is mainly made of stainless steel, which has a relatively large self-weight and cannot meet the requirement of lightweight design. To address these limitations, this paper presents a novel lightweight aluminum alloy load-bearing underframe with the alternative thin-walled energy absorption component, which can both satisfy the function of bearing loads and energy absorption. Firstly, the impact tests and numerical simulations are conducted to compare the crashworthiness of the energy absorption component, i.e., the thin-walled square tube made of S304 (abbreviated as S3N4) and aluminum alloy 5083P-O (abbreviated as A3N4). The result shows that S3N4 has higher energy absorption and mean crushing force, and A3N4 is 56.94 % lower than S3N4 in initial peak crushing force and 53.79 % higher in special energy absorption. Then, the aluminum alloy thin-walled tube is adopted on the novel load-bearing underframe and the parameter study on the wall thickness and number of diaphragms for the energy absorption component is conducted. The result reveals that the 5083P-O thin-walled tube with 5 mm wall thickness and 4 diaphragms can provide the stable and ordered deformation mode and high energy absorption. Finally, a real vehicle impact test is conducted to verify the crashworthiness of the optimized load-bearing underframe, which shows that the deformation modes and mechanical responses are consistent with the numerical simulation. The proposed aluminum alloy load-bearing underframe energy absorption structure can be adopted on subway trains. [ABSTRACT FROM AUTHOR]

Abstract As train speed increases, the aerodynamic drag reduction becomes increasingly significant. The aim of this paper is to find out appropriate bogie positions to reduce the drag of a high-speed train. In this paper, based on the three-dimensional steady incompressible Reynolds-averaged N-S equations and the Realizable k - ε two-equation turbulence model, the effects of bogie positions on the aerodynamic performance and near wake of the three-carriage high-speed train are presented. The mesh resolution and methodology are validated against wind tunnel test. The results show that the front bogie position of the head car has a significant impact on the aerodynamic performance of the head car, leading to different aerodynamic drag forces. When the bogie moves towards the rear by 1 m and 2 m, the aerodynamic drag forces of the head car reduce by 7.75% and 10.56%, and the total drag decreases by 5.57% and 6.58%, respectively. [ABSTRACT FROM AUTHOR]

Abstract The snow accumulation on bogies of a three-car grouping high-speed train has been investigated using unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) coupled with Discrete Phase Model (DPM). The accuracy of mesh resolution and methodology of computational fluid dynamics (CFD) are validated against experimental results. The characteristics of flow fields around bogie regions, the snow particles' motion and snow accumulation are analysed herein. Also the computational costs of numerical simulations using URANS and detached eddy simulation (DES) in the present study are compared. The results show that snow particles begin to flow out from the high-speed train bottom as they come to the first bogie region. After that they whirl around, forming a wind-snow flow in the wake region. Bogie 2 experiences the most snow accumulation. Subsequently, the snow covering on the bogie regions decreases along the train length. A comparison of snow accumulation between URANS and DES methods is made, showing the URANS is sufficient to predict this snow accumulation, which only takes up 2/3 computational cost of the DES. The geometry model consisting of a leading vehicle and a 1/3 s vehicle is recommended to investigate the snow accumulation issue on the bogies of the train. Highlights • URANS coupled with DPM has been used to study snow packing on the bogies of a three-car high-speed train. • Distributions of snow concentration and accumulation in different bogie regions are analysed. • Computational costs of different numerical methods and different geometries are compared. • A comparison of URANS and DES is made, showing URANS is a sufficient method to simulate the snow accumulation. [ABSTRACT FROM AUTHOR]

Abstract A new aluminium-plated structure with transition circular arcs used for railway vehicles is presented. Two impact experiments were performed using a test trolley to examine the plastic response and fracturing of the aluminium-plated structure. The results show that the deformation mode of the aluminium-plated structure switches from global plastic bending deformation to local fracturing at the transition circular arc region, which is consistent with the design. Numerical results are presented in terms of deformation modes, force responses and levels of absorbed energy, demonstrating good agreement with the experimental results. From the results of the numerical simulation, fracturing processes and variations in element stress triaxiality are presented. It is found that the stress state of elements affecting the initiation of cracking is of a tension state, while the stress state of elements affecting the end of cracking is of a shear state. A validated finite element analysis of an aluminium-plated structure with right-angled, circular arcs and chamfering transition sections is presented. Plastic and fracture energy levels of the aluminium-plated structure with three transition sections are measured as 2.56, 27.62, and 30.13 kJ and 0.98, 2.41, and 2.16 kJ, respectively, as the second fracturing point. Finally, the finite element analysis illustrates the impact energy effects involving different combinations of trolley mass and velocity, and experimental boundary conditions for varying bolt yield stress and pre-stress levels are defined in the finite element model to investigate the effects of bolted joints on the dynamic responses of an aluminium-plated structure with transition circular arcs. Highlights • Aluminium-plated structure with transition circular arcs for vehicles is designed. • The results of numerical simulations are in good agreement with the experimental results. • Detailed fracture propagation and variations of stress triaxiality are presented. • Impact trolley energy and experimental boundary conditions on plastic response and fracture of the structure is discussed. [ABSTRACT FROM AUTHOR]

Quasi-static axial compression tests were undertaken using a hydraulic testing machine to study the collapse mode and energy absorption capacity of magnesium alloy AZ31B circular tubes. The effects of the tube wall thickness, length, inner diameter and fillings of aluminium foam and honeycomb were investigated. The results showed that the AZ31B tubes tended to fracture rather than deform. Besides the deformation modes of Euler buckling, concertina mode, diamond mode, mixed concertina and diamond mode and the consequent fracture, large segment fracture, sharding and axial splitting were all observed in the tests. These collapse modes of the tubes depended on their material properties and the geometry of the cross-section. The global buckling fracture showed a poor energy absorption capacity. The sharding mode of thicker tubes and the axial splitting mode of thinner tubes outperformed the other collapse modes on the energy absorbing characteristic. The fillings of the aluminium foam and honeycomb could improve the collapse modes and energy absorption capabilities significantly. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on the energy absorption behavior of shrink circular tube under quasi-static loading by experimental and numerical methods. The circular tube is shrunken in radial direction under axial compression by a cone bush. Energy is absorbed by the plastic bending/compression of tube and the friction between tube and cone bush. Quasi-static crushing tests on aluminum alloy circular tubes demonstrate the feasibility of this type of energy absorber. Numerical simulations are performed to investigate tube deformations and driving force – stroke responses, which agree well with experimental results. On the basis of validated numerical model, effects of friction coefficient, cone angle, and tube dimension on driving force response and energy absorption efficiency are investigated by numerical simulations. It is observed that the shape of driving force – stroke curve is significantly affected by cone angle and tube dimension, whereas it is almost not affected by friction coefficient. Friction energy is almost linearly dependent on friction coefficient, and plastic energy almost linearly increases with an increase in cone angle. In addition, the compact tube has a higher energy absorption efficiency. A comparison on the maximum specific energy absorptions of shrink circular tube and expansion circular tube, reveals that shrink circular tube has a higher energy absorption efficiency. [ABSTRACT FROM AUTHOR]

To explore a diverse number of energy absorption methods, this paper presents an investigation of a cutting aluminium tube absorber for railway vehicles. A quasi-static cutting experiment on an aluminium tube is conducted. The finite element models presented in this study are based on experimental tests, and good agreement is achieved between the experimental and finite element results. It is shown that the cutting aluminium tube absorber presents a stable deformation mode. The chip morphologies of the numerical simulation and experimental test results are coincident, demonstrating that failure criteria defined under the material model are effective. Moreover, a parametric study is performed using finite element models under quasi-static loading. It is found that the cutting depth t , cutting depth w and cutting angle α have a distinct effect on the energy absorption ( EA ), mean crushing force ( MCF ) and peak crushing force ( PCF ) of the absorber. Sobol’ sensitivity analysis is employed to analyze the effects of the design parameters ( t , w , and α ) on the objective responses ( EA and PCF ) based on a polynomial response surface model. It is found that at a larger cutting depth, the increases in EA and PCF are larger. Additionally, to optimize the crushing performance of the absorber, a multi-objective optimization is applied to achieve the maximum EA and minimum PCF values. The results show that EA increases with increasing PCF and at the optimal point B ( EA = 78.29 kJ, PCF = 341.88 kN), and thus, a balance between EA and PCF is obtained. [ABSTRACT FROM AUTHOR]

This paper presents a novel energy absorber that can generate a larger deformation stroke than its free length. The effective crushing distance rate (ECDR) of this structure can exceed 1. During collision, the impact kinetic energy is dissipated by the elastic-plastic deformation of a steel plate and aluminium honeycomb. The bending theory of the steel plate is analysed to estimate the energy absorption (EA) and the mean crushing force (MCF). Then, a finite element (FE) model of the energy absorber is established, and its accuracy is validated by the theory of plate blending. When the plate thickness is 2 mm and 5 mm, the error between the simulation and theoretical results are 1.93% and 3.05%, respectively. The FE model is used to investigate the crashworthy performance. When the new absorber is deformed, the influence of the type of aluminium honeycomb, steel plate thickness and width, guide wheel radius, and number of guide wheels on energy absorption are analysed. Aluminium honeycomb with appropriate parameters can significantly reduce the peak crushing force (PCF) by up to 60.8%. The crushing force (CF) and EA increase as the plate thickness, plate width, and number of guide wheels increase but decreases as the guide wheel radius decreases. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of a new type of energy absorber that works on the principle of active–passive integration. The absorber consists of a crush tube, anti-climber gear, die, support tool, guide tube, and reversible actuator. Before collision, the crush tube of the absorber is extended duo to the effect of the reversible actuator, which breaks through the coupler restrictions on the longitudinal dimension of the absorber and significantly increases the deformation stroke of the absorber. During collision, the kinetic energies are dissipated by the cutting of the circular aluminium or steel tube, shear sliding, and friction between the circular tube and the die. An extension and retraction test, as well as a quasi-static cutting test of crush tubes made of two kinds of materials with different cutting depths of the absorber are conducted. The experimental results show that the active–passive integration energy absorber performs energy absorption effectively. Comparing the energy absorption between the aluminium and steel tubes, the cutting deformation mode of the aluminium tubes is more stable than that of the steel tubes, and the axial cutting force increases with increases in strength of the crush tube material and crush tube cutting depth. Finally, the new type of absorber is applicable to a variety of types of railway vehicles. [ABSTRACT FROM AUTHOR]

• A novel extension of smoothed Finite Element Method (S-FEM) to solve three-dimensional non-Newtonian blood flow. • The semi-SUPG/SPGP stabilization method based on S-FEM for non-Newtonian flows is developed. • S-FEM shows remarkable robustness for the distorted mesh. • Analysis of the performance of S-FEM on non-Newtonian blood flows. Smoothed Finite Element Method (S-FEM) has drawn increasing attention in the field of computational fluid dynamics (CFD) and the present work seeks to make further contribution to this growing field of S-FEM by simulating for the non-Newtonian blood flow. This investigation took the form of Streamline Upwind Petrov-Galerkin in conjunction with Stabilized Pressure Gradient Projection (SUPG/SPGP) to alleviate the spatial oscillation and instability problems. The validation of the cell-based S-FEM (CS-FEM) combined with SUPG/SPGP was carried out by the blood flow over a backward-facing step. The performances of the presented method were explored by the blood flow in the carotid bifurcation and blood flow in the intracranial segment of internal carotid artery. Impressively, the results exhibit good features of the CS-FEM on solving severely distorted mesh vis-a-vis the standard finite element method (FEM). The presented method could realize the accurate prediction in the mentioned complex blood flows as the same as Finite Volume Method software STAR-CCM+. [ABSTRACT FROM AUTHOR]

This paper presented the structure of a crashworthy railway vehicle driver's cab and its crashworthy performance was investigated by experiment and simulation. Based on the structural characteristics of railway vehicle, the driver's cab was divided into three parts: the first part consisted of four thin-walled square tubes with diaphragms, the second part consisted of a front baffle, a first level support structure, a first level draft sill and a first level longitudinal beam, the third part consisted of a second level support structure, a second level draft sill and a second level longitudinal beam. The quasi-static compression experiment showed that the driver's cab produced stable and ordered plastic deformation. Finite element simulation by LS-DYNA was used to simulate the deformation of the structure under quasi-static compression. Simulation results showed good agreement between experiment and simulation, the driver's cab absorbed 2321.13 kJ energy in the quasi-static crushing load, the percent of the first part, the second part and the third part are 17.86%, 81.28%, 0.86%, respectively. Then based on the validated finite element model, a multi-objective optimization was applied to improve the crashworthiness of the driver's cab. It was found that the energy absorption ( EA ) increased with the increasing of crushing peak force ( CPF ), and the minimum EA and CPF in the design range were 4.311×10 3 kJ, 7.609×10 3 kN, respectively, the maximum EA and CPF in the design range were 6.380×10 3 kJ, 15.720×10 3 kN, respectively. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical investigations of a new type of combined energy absorber which working on the principle of expanding and splitting of the circular steel tube. In the first phase of deformation the tube is expanded by the cylinder part of the die. Second phase of deformation characterizes splitting of the expanded part of the tube into strips along the initial sawcuts by the cone part of the die. The strips bend outwards with certain radius to the end of the second phase. Quasi static compression test shows that this type of energy absorber is completely feasible and the combined absorber has 95.34% higher maximal force in compare with absorber which uses only expansion process of deformation. Using this system of deformation, the total energy absorption is obtained by the three mechanisms: elastic–plastic bending of the tube, splitting of the tube wall and friction between the tube and the die. The effect of friction coefficient is studied by simulation, it is found that the effect on friction energy is significant but negligible on splitting energy and plastic energy. [ABSTRACT FROM AUTHOR]

Based on the splitting and bending of a steel plate, a new type of energy absorption structure is presented in the paper. The absorber consists of a steel plate, die, and support tool. During collision, the steel plate is split and bent by the die. Using this type of absorber, energy absorption occurs through the splitting of the steel plate, elastic–plastic bending, and friction between the steel plate and the die. Two kinds of steel plates with different thicknesses are constructed and tested. The experimental results show that the deformation of the steel plates is stable. The grooves on the end of the steel plate effectively eliminate the initial peak of the force. This combined method performs energy absorption effectively. The energy absorption responses of the structure are also analysed using the finite element method. By comparison with the experimental results, the numerical results are validated. [ABSTRACT FROM AUTHOR]

When a high-speed maglev train enters a tunnel, the pressure around it rises and changes quickly. This may lead to serious damage of the train and tunnel structures. With increases of train speed, up to 600 km/h, this issue will become worse. In this study, the three-dimensional, compressible, unsteady, k - ϵ two-equation turbulence model and sliding grid technologies were used to study the effect of train speed on the pressure waves induced by a maglev train passing through a tunnel. The numerical simulation method used was validated against results from moving model tests and semi-empirical formulations. The maglev train modelled was specified to pass through a 2 km tunnel with speeds in the range from 400 km/h to 600 km/h. The surface pressure distribution of the train and tunnel were found and are discussed. The transient pressures on the maglev train and tunnel surface are shown to have a significant relationship with the train speed. Generally, the maxima of the train surface pressures follow the power law relationship with an exponent of 2.35 to the train speed, while for the tunnel surface pressure, an exponent of 2.46 is obtained. The gradient of the initial compression wave at the tunnel entrance follows a power law relationship with an exponent of 3.51 to the train speed, while at the exit this rises to an exponent of 4.99. The amplitude of the micro-pressure wave follows a power law relationship with an exponent of 5.00 to the train speed. Having such data will provide essential support for the design of both the maglev train and tunnel. • Influence on tunnel aerodynamic effects induced by a high-speed maglev train passing through a tunnel has been studied. • Interesting sub-reflection waves induced by train motion in tunnel meeting reflection waves from portals are observed. • Power-law exponents of the relationship between train speed and pressure amplitude are higher than those in previous studies. • Amplitudes of micro-pressure waves follow the power law relationship with an approximate exponent of 5.00 to the train speed. [ABSTRACT FROM AUTHOR]

Abstract: The energy absorption responses of conventional tubes and tubes with diaphragms are analysed here by means of finite element simulation. Numerical results show that tubes with diaphragms exhibit a relatively stable crushing process. The effect of imperfect energy absorption responses is also analysed, including the top shape of tubes and oblique loading. The strain rate affects the dynamic response of tubes with diaphragms. Four prototypes of these tubes were constructed and tested; however, sizeable differences were obtained between experimental results and the results of numerical simulation of the ideal structure in terms of process errors. [Copyright &y& Elsevier]

This paper presents an investigation into the energy absorption behaviour of splitting multiple circular tubes by theoretical, experimental and numerical methods. A theoretical solution for the steady-state crushing force of splitting multiple circular tubes is derived by applying the deformation theory. To explore the energy absorption of splitting multiple circular tubes and to validate the finite element model and a theoretical solution for the crushing force, an impact experiment is performed using a test trolley to examine the splitting process and force responses of multiple circular tubes. The finite element models of splitting multiple circular tubes are then established to investigate the energy absorption behaviour of the structure. The numerical simulation results agree well with those of the impact experiment. The energy absorption of splitting multiple circular tubes with different geometrical configurations, including the wall thickness of the tubes, number of tubes, radius of the tubes and conical angle of the dies, is analysed using a validated finite element model. The results show that the geometrical configurations of the tubes and conical angle of the dies have a distinct effect on the energy absorption. An analysis is also conducted to investigate the energy absorption by the evolution of the theoretical models. It is confirmed that the theoretical solutions provide a reliable prediction of the steady-state crushing force of splitting multiple circular tubes. The effect of the velocity is investigated, and the result shows that the steady-state force increased as the impact velocity increased. • An energy absorber of splitting multiple circular tubes is proposed for railway vehicles. • A theoretical solution for the steady-state force of splitting multiple circular tubes is derived. • Steady-state forces of the numerical simulations and theoretical predictions agree with those of the experiment. • Effect of the geometrical configurations and impact velocity on energy absorption of splitting multiple circular tubes are discussed. [ABSTRACT FROM AUTHOR]

The axial splitting of thin-walled tube is usually considered as an efficient deformation mode to dissipate impact energy thanks to its large stroke ratio. However, the low crushing force and the unstable deformation process, such as crack merging and branching, significantly limit its application in crashworthiness design. In this paper, we propose to enhance the deformation stability through introducing initial kerfs on the inner and outer surfaces of the circular steel tube in its axial direction to guide the propagation of cracks during the splitting process, thus we can improve the crushing force via a significant increase in tube wall thickness. To demonstrate the feasibility of the proposed method, quasi-static compressive experiments on single tube (inner radius r = 55 mm, wall thickness t = 5 mm) and doubled tube (consisted of two tubes with wall thickness t = 5 mm) with kerf depth δ = 0.5 mm split by a radiused die are performed, which exhibit stable deformation processes and high steady-state compression forces (103.32 kN for single tube, and 216.44 kN for doubled tube). Then, finite element simulations are conducted to model the tested samples. It is found that the experimentally observed deformation processes are well captured by simulations, and the relative errors of numerical steady-state compression forces in comparison to experimental results are 0.39% (single tube) and 1.90% (doubled tube), respectively. Finally, based on the validated numerical model, the influence of tube and die dimensions on its crashworthiness performance is discussed. It is observed that the axial load significantly depends on kerf depth, crack number, and tube thickness. The curling radius is nearly not affected by kerf depth, but it almost linearly depends on die radius. Moreover, the tube with larger wall thickness has a higher specific energy absorption. • The crashworthiness of circular tube during axial splitting process is enhanced through introducing initial kerfs on tube surfaces. • Thicker steel tubes with initial kerfs are experimentally demonstrated to have stable splitting processes and high crushing forces. • The introduction of oblique notches significantly weakens the crushing peak force without losing steady-state force. • Effect of the tube and die dimensions on its crashworthiness performance is numerically investigated. [ABSTRACT FROM AUTHOR]

• Experiments and numerical transmittance analysis of wave propagation for proposed 3D EM plates shows excellent consistency. • Effect of structural parameters on bandgap position is investigated. • The bandgap frequency can be reduced by up to 50 % by adjusting structural parameters. • A programmable EM plate is proposed and demonstrated numerically. This paper studies the propagation of elastic waves in a four-leaf clover shaped elastic metastructure (EM), which consists of periodically distributed solid blocks connected by slender beams. The bandgap structure and vibrational transmittance of four-leaf clover shaped EM plates were examined using two-dimensional (2D) and three-dimensional (3D) solid elements. The comparison of elastic wave propagation experiments and numerical transmittance attenuation analysis shows excellent consistency and efficient wave regulation. Based on the experimentally validated model, the effect of structural parameters on the bandgap distribution is explored. It is found that the bandgap frequency can be lowered by up to 50 % and widened by 22 % by adjusting structural parameters, providing useful guidance for parameter settings to lower or widen the low-frequency bandgap. Finally, a programmable EM plate capable of guiding elastic wave propagation is proposed, which has the advantages of convenient adjustment and reliable structure, altering the bandgap from "on" to "off" by adjusting the distribution of the local resonators in the unit cell. Numerical demonstrations and experimental verifications are further carried out, illustrating that the proposed EM plate is capable of highly tuning elastic wave propagation. The results of the study indicate that the four-leaf clover shaped EM has a lower and wider bandgap adjustment range, which can realize waveguide control in a broadband range. The current findings provide important insights for the design of alternative devices such as vibration isolators, beams, and plates. [ABSTRACT FROM AUTHOR]

The massive heat dissipation demands of the brake system in high-speed trains pose a significant obstacle to achieving higher operation speeds. Phase change material has attracted considerable attention in various fields due to their exceptional heat dissipation capabilities, yet their utilization in the brake system of high-speed trains remains unexplored. This study aims to investigate the feasibility of phase change material application in the brake system of high-speed train. Specifically, in Case A, the introduction of phase change material resulted in a notable 21% decrease in the average temperature and a remarkable 40% reduction in the maximum temperature difference within the brake system. The latent heat of the phase change material plays a crucial role in maintaining a substantial temperature differential between the cooling components and discs, thereby enhancing heat flux in the brake system. Phase change materials exhibit superior cooling performance compared to traditional air cooling methods in the brake system. To expedite the cooling process of phase change material and facilitate its transition from liquid to solid, an optimized brake system structure utilizing phase change material was proposed. This optimized design holds promise in enhancing the overall heat dissipation efficiency of the high-speed train brake system. [ABSTRACT FROM AUTHOR]

• A phase-locked measurement method for sweeping jets is established based on low-rate PIV devices. • Unsteady features of sweeping jets and secondary flows in a quiescent condition are visualized. • The effects and mechanism of sweeping jet acting on afterbody vortices are well detected. Although low-operation-rate particle image velocimetry (PIV) provides a good spatial accuracy in measurements at relatively affordable costs, it faces some challenges in capturing unsteady features of oscillatory flow. In this paper, a single sweeping jet actuated to control afterbody vortices from a 30◦ slanted-base cylinder is investigated at a Reynolds number of 87,000. Phase-locked stereo PIV measurements combining triggering reference obtaining and real-time processing via field programmable gate array (FPGA) are leveraged to reveal the unsteady characteristics of the sweeping jet. The examined cases show that the phase-locked method can well identify jet's spatiotemporal development process in each oscillation cycle. A sinusoidal-like interaction along phases between the jet and the afterbody vortex can be reasonably detected. At each moment, coherent small vortical structures form at the upper and bottom jet/ambient interfaces, which are caused by Kelvin-Helmholtz instability. Since the induced vortex has the same rotation direction as the afterbody vortex on each side, they merge with each other as the jet approaches the vortex, causing an increase in vorticity. Meanwhile, the sweeping jet's intrusion into the vortex region induces a rise in turbulent kinetic energy in that area, causing turbulence ingestion of the vortex which weakens the velocity gradient. The sweeping behavior of the jet dominates the afterbody vortex to meander as the jet pushes its way underneath the vortex. The findings of this study provide encouraging evidence for future applications of sweeping jets in control of afterbody vortices. [ABSTRACT FROM AUTHOR]

Polyurea coatings have been widely promoted in explosion and ballistic impact protection applications due to their excellent hyper-elasticity performance. In rail transportation, high-speed trains face potential impact threats from track ballast, which can affect the strength performance of the base material. To address these challenges, we examined the ballistic performances of aluminum alloy plates with polyurea coatings under large-scale impact (>30 mm). Four different configurations of target plates were investigated: A, P-A, A-P, and P-A-P. We fabricated samples and performed dynamic impact tests using an air cannon system to demonstrate the feasibility. Results show that ballistic performance is significantly improved by applying polyurea coatings on aluminum alloy plates. In particular, the growth rate of limit velocity of configuration A-P, P-A, and P-A-P to that of configuration A are 5.5 %, 19.4 %, and 22.8 %, respectively. The enhancement mechanism was further uncovered through stress wave propagation analysis and lateral energy diffusion effect. Explicit formulas for predicting the limit velocity and residual velocity were derived and demonstrated with reasonable accuracy over a wide range of parameter spaces. The observed enhancement in ballistic performance through polyurea coatings on aluminum alloy plates offers promising ways to design and implement more resilient and impact-resistant high-speed train structures. [ABSTRACT FROM AUTHOR]

The turbulent flow past a simplified Intercity-Express 3 high-speed train at R e H = 6 × 10 4 is investigated by a combination of wind tunnel experiments and numerical simulations using the large-eddy simulation (LES), the improved delayed detached eddy simulation (IDDES) and the unsteady Reynolds-averaged Navier-Stokes (URANS) simulation. This work aims to compare the predictive capabilities of LES, IDDES and URANS for the flow over a streamlined high-speed train. Numerical simulations are compared to experimental data for validation. Results show that the well-resolved LES is more accurate among the numerical methods used. Compared to the well-resolved LES, IDDES and URANS using the coarser mesh can produce similar mean flow, although IDDES and URANS are found to be slightly inaccurate for the coherent wake structures near the wall. However, for the near-wall flow instability concerning wake dynamics, Reynolds stresses, turbulence kinetic energy and the fluctuation of pressure, IDDES is found to be inapplicable. Overall, this study suggests that the well-resolved LES is appropriate to the flow of a streamlined high-speed train. Moreover, IDDES and URANS are proved to apply to the mean field of the studied flow. • Well-resolved LES is applied to the flow induced by a streamlined high-speed train. • IDDES and URANS using coarse computational grids are reliable in the prediction of mean flow for the high-speed train. • IDDES is inapplicable for the near-wall wake instability. [ABSTRACT FROM AUTHOR]

Under weather conditions such as snow and icing in cold regions, snow and ice accumulation on bogies severely affect the running safety and increase the energy consumption of urban rail trains. To analyze the snow and ice accumulation process, experiments for real urban rail train non-powered bogie were conducted for the first time in the Central South University Icing and Snowing Wind Tunnel (CSU-ISWT). Two anti-snow structures (deflectors and wheelset snow shields) with low energy consumption were designed and discussed based on comparative experiments. The following data were collected after each experiment: dynamic accumulation process, final distribution of snow and ice, and total accumulation mass on the bogie. The results showed that the distributions on the original and optimized bogies were similar. Much more snow and ice accumulated on the lower part of the bogie than on the upper part and covered more on the windward side of the frame than on the leeward side. In the experiments with anti-snow structures, the snow and ice mass accumulated on the bogies decreased by 53.35% and 52.64% in the deflectors and wheelset snow shields cases, respectively. The proposed structures were proven to significantly improve anti-snow performance on the bogies. Therefore, the presented initial research can remarkably strengthen the transportation capacity and safety of urban rail trains in winter. • The snow and ice accumulation experiments for bogie were conducted in the CSU-ISWT. • Two anti-snow structures were designed and discussed by comparative experiments. • The accumulation process, final distribution and mass on the bogie were analyzed. • Mass accumulated on the bogie was decreased by 53.35% and 52.64%, respectively. [ABSTRACT FROM AUTHOR]

• The effect of strain rate on dynamic splitting loading of combined circular tubes are studied analytically and their results are validated by FE simulations. • Impact experiment results show that the combined circular tubes energy absorber experience steady dynamic splitting deformation. • Multi-objective optimization for combined splitting circular tubes energy absorber is performed under the eccentric collision distance of H = 40 mm. This paper proposes a new type of combined splitting circular tube energy absorber for subway vehicles. An impact experiment is conducted to investigate the dynamic crushing performance of this combined splitting circular tube energy absorber. The results show that the combined tubes experience steady dynamic splitting deformation. The crush force efficiency (CFE) and effective stroke ratio (ESR) of the combined splitting circular tube energy absorber are 85.7% and 85.9%, respectively. A theoretical solution for the dynamic splitting crushing load is derived. Finite element (FE) models of the energy absorber are then established, and the dynamic crushing forces agree well with those of the impact experiment. The cumulative error and validation metrics of the crushing force obtained from the numerical simulation and impact experiment are 0.0938 and 0.9122, respectively. The effect of the strain rate of AISI 1020 steel on dynamic steady-state forces is analytically studied, and the results are compared with those of FE simulations and impact experiments. The numerical results show that the dynamic steady-state force of the combined splitting circular tubes under dynamic loading increases by 31.69% compared to that of the tubes under quasistatic loading. The effects of various structural parameters are discussed using the validated FE models. The results show that the combined splitting tube energy absorber has excellent crashworthiness under eccentric loading. The eccentric impact of the two absorbers has a significant influence on the crashworthiness performance of the structure. The specific energy absorption (SEA) increases by 15.2% as the eccentric distance increases from 20 to 80 mm. Compared with the influence of the wall thickness t of the combined splitting circular tubes, the tube radius and die angle have a more significant influence on the SEA. To improve the crashworthiness of combined splitting circular tubes under eccentric loading, a Pareto front of the SEA and average axial crushing force (AACF) under an eccentric distance of H = 40 mm was obtained after optimization by multiobjective particle swarm optimization (MOPSO). The results show that the SEA and AACF are positively correlated and that a balance between the SEA and AACF was obtained at optimal point B (SEA = 14.6 kJ/kg and AACF = 938 kN). [ABSTRACT FROM AUTHOR]

• The proposed CS-FEM phase-field is an efficient fracture modelling in elasto-plastic solids. • The computational cost is slightly lower than the finite element counterpart. • Complex crack paths are simulated without any ad hoc criterion. • Resultant crack patterns are in excellent agreement with experimental observations. Three-dimensional (3D) phase-field models based on the cell-based smooth finite element method (CS-FEM) are established in this paper. The present model consists of three key ingredients: 1) a phase-field model of fracture in elasto-plastic solids, 2) a staggered scheme for nonlinear interactions between the phase-field equations and those for the elasto-plastic solid mechanics, and 3) its underline solution platform of the cell-based smoothed finite element method, CS-FEM. The phase-field model allows effective capturing of the evolution process of complex fracture morphology in elasto-plastic solids. The use of the staggered algorithm gives a practical means to couple the phase field and displacement field in fracturing elasto-plastic solids. The CS-FEM offers important softer model behavior in solving the governing equations. For wide applicability of our Phase-field CS-FEM approach, it is implemented in the commercial software ABAQUS via User Defined Element (UEL) subroutine. Numerical examples of both 2D and 3D benchmark problems with complex crack topologies are presented to verify the accuracy of the solutions. Good agreements are obtained with the experimental observations and existing numerical results in the literature. The phase-field CS-FEM approach offers an effective alternative means to model 3D fracturing in elasto-plastic solids. [ABSTRACT FROM AUTHOR]

The synergistic effects of sweeping jets (SWJs) hold significant potential in controlling afterbody vortex flows of a cargo fuselage. A combination of SWJ pairs, located at various streamwise positions, are employed to investigate the efficiency of their synergy in influencing the afterbody flows of a slanted-base cylinder with a 30° angle at a Reynolds number of 200,000. The total mass flow rate is kept similar resulting in a variation of the momentum coefficient of SWJs from C μ =4.3×10−3 to 1.0×10−1. Energy efficiency and mass flow interactions were examined through direct force measurement, stereo Particle Image Velocimetry (PIV), and surface pressure measurement. The results show that the jet impingement on the surface is stronger when there is synergy among SWJs positioned more upstream (e.g. the combination of Top and Mid pairs), particularly at low momentum coefficients (C μ < 0.02); conversely, when considering the synergy of SWJs located more downstream (e.g. the combination of Mid and Bot pairs), a greater reduction in surface pressure is observed at higher momentum coefficients (Cμ > 0.05); a potential net energy saving is achieved in the case of the combination of Top, Mid and Bot pairs (T+M+B). The controlled vorticity distribution observed in the collaborative configurations was mostly sandwiched by curves of individual SWJ cases, which is due to the fact that downstream SWJs (located at Mid and Bot positions in case T+M+B for instance) manage to weaken the enhanced vortex induced by the SWJ at upstream (located at Top position), highlighting a compromise in the synergy effectiveness of the jets with reverse roles at different positions. However, by taking the similar advantages of SWJ at certain positions on the vortex control, at C μ =1.7×10−2, the vorticity reduced by the case combining Mid and Bot pairs is even 7 % and 13.5 % greater than cases Mid and Bot, respectively, which could serve as a hint on the potential benefit of SWJs' synergy in the future. [ABSTRACT FROM AUTHOR]

Abstract The aim of the present work was to study the synergistic reinforcement, by short and continuous carbon fibers, of polyamide-based composites. The three-phase composites were obtained by the fused filament fabrication process where short fiber reinforced polyamide was deposited/printed along with continuous carbon fibers in a layered structure. The properties of the continuous carbon fiber tows and short carbon fiber reinforced polyamide tows were first evaluated by means of morphological, thermal and mechanical tests. The effects of stacking sequence of laminates as well as the effects of both short and continuous fibers' contents, on the mechanical properties of laminated composites, were carefully analyzed by considering several layering configuration. The results showed that the synergistic reinforcement of laminates by both short and continuous carbon fibers was indeed superior to the individual carbon fiber reinforcement for the tensile strength but not for the elastic modulus. The tensile properties of the laminated composites were higher when the stacked continuous carbon fiber reinforced layers (CCFRLs) were separated. Laminated composites with more interfaces between short carbon fiber reinforced layers (SCFRLs) and SCFRL/CCFRL interfaces showed higher mechanical performance due to the stronger adhesion of these interfaces compared to the interfaces between CCFRLs. The mechanical properties of laminated composites tended to be higher with increasing continuous carbon fiber content. The rule of mixture was used to estimate the mechanical behaviors of short and continuous fiber reinforced composites. All the experimental data was comprised between the upper bound and the lower bound estimates. However, the experimental results were rather close to the upper bound due to the alignment of the continuous carbon fibers. [ABSTRACT FROM AUTHOR]

Abstract The objective of this study is to investigate the fracture behaviors of windshield laminated glass for high-speed trains. For this purpose, tempered glass specimens sampled from constituent components of polyvinyl butyral (PVB) laminated windshield panes were tested using the following tests: flexural strength test, quasi-static uniaxial tensile test, low strain rate compression test and dynamic compressive test with split Hopkinson pressure bar (SHPB). Together with simulations, the testing results were used to determine the constitutive constants of the Johnson-Holmquist ceramic (JHC) model, including the equation of state, the strength criterion and the strain-rate effect. To validate the JHC model, it is used to simulate a safety hammer impact test on PVB-Laminated tempered glass (PVB-LTG). The simulation results showed that the JHC model with tempered material constants for PVB-LTG successfully predicted the impact response of windshields. The practical implications of fragmentation and cracking are also discussed. [ABSTRACT FROM AUTHOR]

The present study aims to assess the prediction ability of URANS (unsteady Reynolds-averaged Navier-Stokes), SAS (scale-adaptive simulation), and IDDES (improved delayed detached-eddy simulation) on the naturally asymmetric flow of a generic ship model. The inlet velocity gives a Reynolds number of 8 × 104 based on the ship width. Experimental results are used as the baseline to judge the accuracy of these modelling techniques. The findings indicate that all techniques can predict the flow asymmetry of the ship wake, although URANS is less accurate due to its inability to resolve small-scale flow structures. Furthermore, IDDES is found to be more accurate than SAS considering the extent of wake asymmetry. Therefore, IDDES is recommended when higher accuracy is needed despite its higher computational demand. • The predictive ability of URANS, SAS and IDDES on the naturally asymmetric flow of a generic ship model is assessed. • All the three techniques used can predict the flow asymmetry, although URANS is less accurate. • IDDES is more accurate than SAS considering the extent of wake asymmetry. [ABSTRACT FROM AUTHOR]

The significant increase in train speed contributes to stronger vehicle/tunnel coupling aerodynamic effect, especially on the intensity of the micro-pressure wave (MPW) emitted at high-speed maglev tunnel exit. Hence when the train speed reaches 600 km/h and more, how to effectively mitigate the MPW becomes a challenge for aerodynamic researchers. In this study, a novel vented tunnel hood with the decreasing open ratio along the enlarged cross-section wall was proposed, while one consistent and two inconsistent layouts of the hoods applied at the tunnel portals were attempted to obtain a better hood combination for the mitigation of MPW. In addition, the sliding mesh technique was used to simulate the train passing through the single-track high-speed maglev tunnel. The validation of the methodology has been carried out to compare with the previous moving model test results. The peak variations of pressure wave and MPW were analysed in combination with the grid-independence study and numerical validation. The new hoods installed consistently at the tunnel portals (entrance and exit), can reduce the maximums of MPWs at required locations, i.e., 20m and 50m from the tunnel exit, by 66.9% and 40.9% respectively, when compared to the existing unvented tunnel hood; however, when the new hood at the tunnel exit is replaced by the existing tunnel hood without vents, the maximums of MPWs at the corresponding 20m and 50m are significantly increased by 79.1% and 71.0%. After changing the set-up of the inconsistent hoods, i.e., the tunnel entrance hood is unvented and this novel hood is installed at the tunnel exit, the corresponding MPW peaks can be reduced by 84.0% and 71.1%. Therefore, the hoods at both of tunnel entrance and exit can affect the variations of MPWs, and a reasonable arrangement of the hood openings at tunnel portals can effectively mitigate the MPW emitted at the high-speed maglev tunnel exit. • A novel vented and enlarged cross-section tunnel hood with the decreasing open ratio was proposed. • One consistent and two inconsistent layouts of hoods were used for the reduction of micro-pressure wave amplitudes. • The mitigation mechanism of the new hoods with different set-ups at tunnel portals has been revealed. [ABSTRACT FROM AUTHOR]

In this paper, the snow accumulation on the bogies of high-speed trains has been investigated using a numerical simulation method based on the unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) coupled with the Discrete Phase Model (DPM). The effects of bogie cut outs’ shape, running speed of high-speed trains and snow particle density and diameter on the snow accumulation and particle movement characteristics are discussed. The results show that the bogie installation region with inclined plates shows better anti-snow performance than the configuration with straight plates, which greatly affects the flow structure and snow concentration distribution in the upper space of bogie regions. The running speed of high-speed trains has dominant effect on the snow accumulation on the bogies, and the snow accumulation issue of bogie becomes more serious with increasing running speed. Furthermore, the snow particle density and diameter also have large influence on the snow accumulation on the bogies. With the increase of snow particle density and diameter, the flow range at height direction around bogie region of snow particles become lower and the quality of snow accumulation decrease significantly. [ABSTRACT FROM AUTHOR]

The aerodynamic drag of a high-speed train can contribute significantly to its energy consumption. Hence, the purpose of this paper is to find out a new compound mode of bogie cut outs to achieve drag reduction for a Chinese high-speed train. In this paper, a Detached Eddy Simulation method based on the Realizable k - ε turbulence model was used to investigate the underbody flow features of high-speed trains with different compound modes in the angles of bogie cut outs at Re  = 1.85 × 10 6 . The time-averaged aerodynamic drag was compared with experimental data from wind tunnel tests. The results show that the DES simulations present high accuracy in predicting this kind of flow underneath the train body, and those numerical results closely agree with the experimental data. The variations of bogie cut outs' angles only cause the changes of flow structures around the bogies and in the wake. As a result, obtain different aerodynamic drag forces. Most of drag of the train is experienced by the streamlined head and all bogie regions. A new compound mode of bogie cut outs is proposed in the present paper, achieving 2.92% drag reduction for a three-car model. [ABSTRACT FROM AUTHOR]

Misalignment is a prevalent problem in rotor machinery. This paper proposes a numerical analysis for the mixed EHL of finite-line contacts considering tilting loads based on FEM. The Reynolds and linear elasticity equations, and Greenwood-Tripp contact model are coupled in an iterative process to solve the fluid-solid/solid-solid interaction under the compound external force and moment. Lubrication characteristics at both ends of the cylinder are analyzed and an asymmetric profile design scheme is presented to improve the lubrication performance at the cylinder's lower end. It is found that proper profile parameters can reduce EHL pressure by 40%, increasing the minimum oil film thickness by up to 100%, and thus reduce asperity contact pressure by up to 50%. • An FE model for the mixed EHL analysis of finite line contacts is developed. • The compound loading condition including the external force and moment is considered. • Lubrication characteristics of tilted finite line contact are analyzed and disclosed. • The asymmetric profile design scheme is proposed to improve lubrication performance. [ABSTRACT FROM AUTHOR]

The study of the ship airwake is critical as it explores the effect of unsteady wake flow on helicopter operations. This paper studied the near-wake flow topology of a generic ship at Re = 8 × 104 to assess the capability of a hybrid RANS/LES (Reynolds-averaged Navier–Stokes/large-eddy simulation) approach, known as IDDES (improved delayed detached-eddy simulation). The impact of computational parameters, including the mesh grid, residual level, time-step size, momentum discretization scheme and transient formulation, on the wake flow was investigated. The numerical results were validated by using the previous experimental data and LES results. The results show that except of the mesh resolution all other computational parameters varied in the current study do not have significant effect on the global drag forces, but showing large differences on the prediction of the local wake flow structures. This point has not been evidently reported in the previous work. The finer grid resolution is sufficient to produce an accurate qualitative and quantitative prediction of the flow structures, while using a poor grid resolution (coarse mesh) leads to inaccurate prediction of the flow topology. The recommended parameters for the time-step size (7.5 × 10−5s) and residual level (1 × 10−4) provide sufficient accuracy of wake predictions, showing good agreement with reference studies. For the convective term of the momentum equation in IDDES, the bounded central differencing scheme is proposed for its discretization, while the bounded second-order implicit is proposed to be adopted as the transient formulation. • The ability of IDDES to predict the bi-stable phenomenon of a generic ship has been evaluated. • The effect of computational parameters on the ship flow topology has been studied. • IDDES results show good agreement with available numerical and experimental data. • Consistency of global quantities can not guarantee the same trend for the local flow topology. • Optimum computational parameters are proposed for the study of the bi-stable ship wake flow. [ABSTRACT FROM AUTHOR]

[Display omitted] • The high-speed maglev train/tunnel coupling aerodynamic characteristics has been studied. • A novel arch lattice-shell of enlarged cross-section hoods has been proposed. • Propagation and evolution properties of initial compression waves have been clearly illustrated. • The mitigation mechanism of the arch lattice-shell has been revealed. With technology development of 600 km/h high-speed maglev trains, how to effectively alleviate the transient pressure wave problem caused by such a high-speed maglev train passing through the tunnel is significantly of importance. In this paper, based on the three-dimensional, unsteady, compressible Navier-Stokes equations and k-epsilon turbulence model, a high-speed maglev train with a speed of 600 km/h was simulated to pass through a single-track tunnel with a cross-sectional area of 92 m2, and the numerical method used was validated by a moving model test. The propagation characteristics of pressure waves in the tunnel and the evolution properties of the initial compression wave were explored. A new enlarged cross-section hood with an arch lattice-shell was proposed. With helps of the semi-closed decompression domain formed by the outer wall of the inner arched plate and the inner wall of the enlarged cross-section tunnel hood, the novel hood can further dissipate the energy of the initial compression wave; thus, the pressure gradient at 140 m from the tunnel entrance and the micro-pressure wave amplitude at 20 m from the tunnel exit can reduce by 32.1 % and 35.6 % respectively, as compared with the existing enlarged cross-section tunnel hood. When compared to the tunnel without hoods, this novel hood can achieve 64.8 % and 74.3 % reduction at the same monitoring points. [ABSTRACT FROM AUTHOR]

The single deformation mode of splitting tube significantly restricts its energy absorption capability. To address this limitation, in this paper we propose a new hybrid absorber with an external die added to the outside of the expanding–splitting tube, thus the circular tube undergoes sequential expanding, splitting, and bending deformations. We fabricate samples and perform quasi-static compressive experiments on the splitting tube, expanding–splitting tube, and proposed hybrid splitting tube. Experimental results show that the hybrid tube deforms in a controlled and ordered way as designed. Remarkably, the steady crushing force of the hybrid tube is 52.1% and 221.6% higher in comparison to that of the same tube with splitting mode, and expanding–splitting mode, respectively. The crushing force responses and deformation processes are well captured by finite element simulations. The relative errors of the steady crushing forces and energy absorption are within 5.0%. A parametric analysis is performed. We show that the structure parameters play an important role in the crashworthiness performance. In particular, the tube with thicker walls has a larger crushing force and a higher specific energy absorption. The small cracking number and spacing between the inner and outer die can trigger unstable deformation. Our results can advance the engineering application of splitting tubes and the lightweight design of energy absorbers. [Display omitted] • A new hybrid energy absorber of expanding–splitting–bending​ circular tube is proposed. • Quasi-static experiments demonstrate the feasibility of the proposed new energy absorber. • Comparisons of experimental and FE results show excellent agreement. • Effect of structure parameter on crashworthiness performance is investigated by a parametric analysis. [ABSTRACT FROM AUTHOR]

A triangular configuration spring–mass model is proposed in this paper to investigate the dependence on structural parameters of elastic wave propagation in two-dimensional (2D) elastic metamaterials/metastructures (EMs). Based on the lattice dynamics, the dispersion relations of the multiple degrees of freedom (DOF) unit cell and the vibration propagation of elastic waves are derived. Moreover, the effects of the configuration angle, spring stiffness, and mass distribution on the frequency and width of bandgaps are explored. The bandgap can be widened by 31.5% or as low as 32 Hz by reasonably adjusting the stiffness and mass distribution. Finally, the asymmetric structure (Model II-1) with the most pronounced full-bandgap difference produced by scanning along two irreducible Brillouin zones (IBZs) of Γ -X-M- Γ and Γ -Y-M- Γ was selected to explore the directional bandgap properties of EM. The dispersion curves obtained by the eigenmode division method are more consistent with the attenuation ranges of the vibration transmittance and can be used to easily and comprehensively identify the bandgap properties. This research provides important clues and theoretical guidance for the design of vibration isolators, beams, plates and other renewed devices. • The dispersion relation and bandgap mechanism are explored analytically. • The dependence on structural parameters of bandgap generation is investigated. • Band structure of the EM with different configuration of local resonator are studied. • The bandgaps can be extended as low as 32 Hz by adjusting the spring stiffness and mass distribution. • The dispersion curves are identified by eigenmodes for directional wave propagation. [ABSTRACT FROM AUTHOR]

The capability of Large Eddy Simulations (LES), Improved Delayed Detached Eddy Simulations (IDDES) and Reynolds-Averaged Navier–Stokes Equations (RANS) to predict the flow behind notchback Ahmed body is investigated in the present paper. Simulations consider two specific models, with effective backlight angles of β 1 = 17.8 ° and β 2 = 21.0 ° , respectively. The focus of the study is on the prediction of the expected lateral asymmetry or symmetry of the near-wake flows. Results show that IDDES using coarse computational grids predicts the flow in agreement with LES using finer computational grids. RANS results in inaccurate flow predictions, attributed to its steady formulation relying on turbulence modelling being incapable of dealing with the studied flow. Modal analysis applying Proper Orthogonal Decomposition (POD) suggests the consistency of the wake dynamics between IDDES and LES. The presence of the wake bi-stability is validated by the wind tunnel experiment. • The first paper assessing LES, IDDES and RANS for flow predictions of notchback vehicles. • IDDES and LES are capable of wake bi-stability prediction. • RANS results in inaccurate flow predictions due to the miscalculated wake separations and reattachments. [ABSTRACT FROM AUTHOR]

This study numerically investigates the effects of Jacobs bogies on the aerodynamic behaviors of a high-speed train using improved delayed detached eddy simulation (IDDES) at R e ​= ​3.3 ​× ​105. The results of the numerical simulations have been validated against the experimental data obtained from a previous reduced-scale moving model test and a wind tunnel test. The slipstream velocity, wake flow, underbody flow and aerodynamic drag of the HST are compared between the conventional bogie case and Jacobs bogie case. The results show that the use of Jacobs bogies can reduce the TSI values of the slipstream velocity at trackside and platform positions by 11.07% and 22.40%, respectively, which thereby shows a positive effect on improving the safety level of trackside workers and passengers standing on the platform. The Jacobs bogies are found to decrease the maximum values of the slipstream velocity and turbulence kinetic energy occurring at the intermediate bogie regions beneath the HST by 30.08% and 41.32%, respectively, which is beneficial for weakening the ballast flight phenomenon. The Jacobs bogies significantly narrow the scale of the longitudinal vortex structure in the wake propagation region. Additionally, the application of Jacobs bogies lowers the aerodynamic drag values of the vehicles and contributes to a 10% total drag reduction. • IDDES is validated to be a good engineering tool for the prediction of unsteady flow field around HST. • The aerodynamic behaviours of conventional HST and Jacobs HST are comparatively analyzed. • The use of Jacobs bogies is beneficial to alleviate the ballast flight phenomenon. • Jacobs bogies can improve the safety level of passengers and trackside workers. [ABSTRACT FROM AUTHOR]

The influence of water spray from wheels on the ice accumulation in the bogie regions of high-speed train has been studied using the coupling numerical methods of improved delayed detached eddy simulation (IDDES) and Lagrangian Model. The rotation of the wheels was simulated using the moving overset grid technique. The flow field, spatial distribution and surface distribution of droplets on the bogies have been analysed to identify the effect of various speed on the movement of droplets. The results show that the inlet speed between 160 ​km/h and 250 ​km/h will lead to the most severe influence on water spray from wheel in the whole bogie regions. A large amount of water droplets gathering on the surface of the bogies and bogie cavities is likely to cause severe ice accretion. The influence of water spray for high-speed train decreases rapidly at the speed of 300 ​km/h and changes a little as the speed continues to increase. Among all the components of the bogie, the brake clamp is most affected by droplets. Furthermore, the droplets were found to have a severe effect on the draft sill and air spring. • The influence of water spray from wheels on the bogie of high-speed train was studied using IDDES, Lagrangian Model and moving overset grid technique. • The study found brake device and draft sill to be most affected by droplets. • The effect of water spray on high-speed train at various speed was found. [ABSTRACT FROM AUTHOR]

Anemometers are usually set up along railway embankments to monitor wind speeds, and the layout for them has to be investigated. This work used an improved delayed detached eddy simulation (IDDES) approach to explore the flow properties around railway embankments, and then a proposal was put forward for the layout of anemometers. The numerical method was validated against previous wind tunnel tests on the speed-up ratios of the flow around a 1/300 scale two-dimensional embankment with the slope gradient of 1:2. The effects of inlet velocity profiles, i.e., uniform velocity and atmospheric boundary layer velocity profiles, on the speed-up ratios around a 5 m high railway embankment were compared. The study indicates that using a uniform velocity profile to assess the operational safety of trains running across strong wind regions could be favourable, especially when complex local terrains contribute to different wind characteristics. The anemometers should be set upstream, i.e., at a well defined distance in locations with sufficient extent of open ground and on the electrification masts along railway lines. This is not in line with the anemometer layout of the existing SWEWS (Strong Wind Early Warning Systems), the difference being due to the speed-up effect of the railway embankment, which is usually not considered explicitly. Formulas have been developed on the basis of regression of the simulation results to express the relationships between e.g. top wind speed over the embankment (located in an area where it is not possible to install anemometers) and measured wind speeds. In this way it is possible to take into account the speed-up effect encountered by the wind passing over the embankment, which needs to be considered in the operational rules in order to ensure safe operations. • Flow properties around railway embankments have been investigated using IDDES. • A spectral synthesizer method was used to generate perturbations at the inlet. • Using a uniform velocity profile to assess the operational safety of trains running across strong wind regions is favourable. • A proposal is put forward for the layout of anemometers. [ABSTRACT FROM AUTHOR]