Numerical study on the slipstream and trackside pressure induced by trains with different longitudinal section lines

2017 ◽  
Vol 232 (6) ◽  
pp. 1671-1685 ◽  
Author(s):  
Taizhong Xie ◽  
Tanghong Liu ◽  
Zhengwei Chen ◽  
Xiaodong Chen ◽  
Wenhui Li
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Longitudinal Section ◽  
Detached Eddy Simulation ◽  
Full Scale Test ◽  
Section Line ◽  
Eddy Simulation ◽  
High Speed Trains ◽  
Scale Test ◽  
Pass Through

Slipstreams are generated when high-speed trains pass through the open air causing safety threat to passengers, trackside workers and infrastructure. This study calculates the slipstream induced by trains with different longitudinal section lines using a detached-eddy simulation. The slipstream velocities and pressure at various lateral distances from the centre of the rail position and various vertical distances from the top of the rail position are calculated at a Reynolds number of 1.8 × 106, and the flow field around the trains is analysed. The results of the calculation are compared with the results of a full-scale test to validate the numerical method adopted in this work. The results demonstrate that the variations in the slipstream velocities induced by the four types of trains are similar as are the variations in the trackside pressures. The amplitudes of the slipstream velocities and trackside pressures are different due to the influence of the longitudinal section line, and both the slipstream velocity and the trackside pressure increase with the slope of the longitudinal section line. The slipstream velocity and trackside pressure decrease with increasing distance from the centre of the rail and the top of the rail. The large difference in the slipstream induced by the four types of trains occurs in regions where the distance from the centre of the rail is greater than 2.5 m and the distance from the top of the rail is greater than 1.5 m, and those regions are also the areas where platform passengers and track infrastructure are located. The results demonstrate that the slipstream in those regions can be reduced by adopting relatively lower slopes of the longitudinal section line.

A numerical study of snow accumulation on the bogies of high-speed trains based on coupling improved delayed detached eddy simulation and discrete phase model

2018 ◽  
Vol 233 (7) ◽  
pp. 715-730 ◽  
Author(s):  
Mingyang Liu ◽  
Jiabin Wang ◽  
Huifen Zhu ◽  
Sinisa Krajnovic ◽  
Guangjun Gao
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Snow Accumulation ◽  
Phase Model ◽  
Detached Eddy Simulation ◽  
Discrete Phase Model ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Flow Mechanisms ◽  
Discrete Phase

A numerical simulation method based on the improved delayed detached eddy simulation coupled with a discrete phase model is used to study the influence of the snow on the performance of bogies of a high-speed train running in snowy weather. The snow particle trajectories, mass of snow packing on the bogie, and thickness of snow accumulation have been analyzed to investigate the flow mechanisms of snow accumulation on different parts of the bogies. The results show that the snow accumulation on the first bogie of the head vehicle is almost the same as that of the second bogie, but the total accumulated snow on the top side of the second bogie is more than 74% higher than that of the first bogie. Among all the components of the bogies, the motors were found to be strongly influenced by the snow accumulation. The underlying flow mechanisms responsible for the snow accumulations are discussed.

A new methodology for the assessment of the running resistance of trains without knowing the characteristics of the track: Application to full-scale experimental data

2018 ◽  
Vol 232 (6) ◽  
pp. 1814-1827 ◽  
Author(s):  
Claudio Somaschini ◽  
Tommaso Argentini ◽  
Daniele Rocchi ◽  
Paolo Schito ◽  
Gisella Tomasini
Keyword(s):  
High Speed ◽  
High Capacity ◽  
Full Scale ◽  
Design Stage ◽  
Resistance Force ◽  
Full Scale Test ◽  
High Speed Trains ◽  
Scale Test ◽  
Full Scale Tests ◽  
Resistance Coefficients

The resistance to motion of trains is an essential requisite especially while designing high-speed trains and high-capacity railway lines. The optimisation of friction effects and aerodynamic performance can be done during the design stage of a new train but the actual value of the running resistance can be inferred only by means of full-scale tests during the operation of a train. A CEN standard (EN 14067-4) describes the methodologies for the assessment of the running resistance of railway vehicles starting from full-scale test measurements. According to this standard, the speed-dependent terms of the resistance force have to be determined by means of coasting tests on railway lines, whose characteristics must be well known. Since this is not always possible and small errors on the gradient could lead to major uncertainties in the evaluation of the resistance force, a new method for the estimation of the running resistance coefficients, irrespective of the characteristics of the track is proposed in this paper. The reliability of the method is verified by comparing the results with those obtained from the procedure proposed in the CEN standard. The comparison shows that the new methodology is able to evaluate the resistance coefficients with an accuracy equivalent to that of the other methods but with fewer tests and with a more robust procedure relying on a lesser number of parameters.

A numerical study of aerodynamic characteristics of a high-speed train with different rail models under crosswind

2020 ◽  
pp. 095440972096925
Author(s):  
Zhiwei Jiang ◽  
Tanghong Liu ◽  
Houyu Gu ◽  
Zijian Guo
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Simulation Method ◽  
Aerodynamic Characteristics ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Pressure Distributions ◽  
Significant Difference ◽  
Aerodynamic Performances ◽  
Yaw Angle

The CFD (Computational Fluid Dynamics) numerical simulation method with the DES (detached eddy simulation) approach was adopted in this paper to investigate and compare the aerodynamic performance, pressure distributions of the train surface, and flow fields near the train model placed above the subgrade with non-rail, realistic rail, and simplified rail models under crosswind. The numerical methods were verified with the wind tunnel tests. Significant differences in aerodynamic performances of the train body and bogie were found in the cases with and without a rail model as the presence of the rail model had significant impacts on the flow field underneath the vehicle. A larger yaw angle can result in a more significant difference in aerodynamic coefficients. The deviations of the train aerodynamic forces and the pressure distribution on the train body with the realistic and simplified rail models were not significant. It was concluded that a rail model is necessary to get more realistic results, especially for large yaw angle conditions. Moreover, a simplified rectangular rail model is suggested to be employed instead of the realistic rail and is capable to get accurate results.

Numerical simulation of the effects of obstacle deflectors on the aerodynamic performance of stationary high-speed trains at two yaw angles

2017 ◽  
Vol 232 (3) ◽  
pp. 913-927 ◽  
Author(s):  
Ji-qiang Niu ◽  
Dan Zhou ◽  
Xi-feng Liang
Keyword(s):  
High Speed ◽  
Simulation Method ◽  
Aerodynamic Performance ◽  
Wake Flow ◽  
Detached Eddy Simulation ◽  
Aerodynamic Forces ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
High Speed Trains ◽  
Yaw Angle

In this study, based on the shear-stress transport κ–ω turbulent model, the improved delayed detached eddy simulation method has been used to simulate the unsteady aerodynamic performance of trains with different obstacle deflectors at two yaw angles (0° and 15°). The numerical algorithm is used and some of the numerical results are verified through wind tunnel tests. By comparing and analysing the obtained results, the effects of the obstacle deflectors on the force of the trains as well as the pressure and flow structure around the trains are elucidated. The results show that the obstacle deflectors primarily affect the flow field at the bottom of the head car as well as the wake flow, and that the internal oblique-type obstacle deflector (IOOD) markedly improves the aerodynamic performance of the trains, by decreasing most of the aerodynamic forces of the train cars and minimising their fluctuations. Further, a nonzero yaw angle weakens or even changes the effect of the IOOD on the aerodynamic forces of the train cars. However, the effect of the IOOD is more on the tail car.

Numerical Study on a Single Square Cylinder Subjected to Vortex-Induced Vibration in HTR-PM

2016 ◽  
Author(s):  
Qiankun Xiao ◽  
Li Shi ◽  
Xiaoxin Wang ◽  
Xiaowei Luo ◽  
Xinxin Wu
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Numerical Study ◽  
Flow Direction ◽  
Turbulence Models ◽  
Detached Eddy Simulation ◽  
Square Cylinder ◽  
Vortex Induced Vibration ◽  
Eddy Simulation ◽  
High Reynolds

The heat transfer tube bundles of the steam generator in high temperature reactor pebble bed module (HTR-PM) are subjected to high speed helium flow, which might lead to vortex-induced vibration (VIV). In the present paper, to investigate the vibration of square cylinder under flow effect, vortex shedding phenomena of a stationary square cylinder at a high Reynolds number equal to 6.8 × 104 is simulated by detached eddy simulation (DES) turbulence models. A comparatively close agreement with previous experimental results is achieved. Combining computational fluid dynamics (CFD) and computational structural dynamics (CSD) methods, a fluid-structure-interaction (FSI) model for VIV of the square cylinder is then established, and vibration response perpendicular to flow direction were investigated. Moreover, the safe range of the natural frequency of the square cylinder to avoid synchronized vibration with VIV is analyzed. The results of this paper can provide an important guidance to the design of the heat transfer tubes and their supports in HTR-PM.

Numerical study of the flow over the modified simple frigate shape

2020 ◽  
pp. 095441002097775
Author(s):  
Tong Li ◽  
Yibin Wang ◽  
Ning Zhao
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Reference Value ◽  
Flow Fields ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

scholarly journals Numerical Investigation on the Influence of the Streamlined Structures of the High-Speed Train’s Nose on Aerodynamic Performances

2021 ◽  
Vol 11 (2) ◽  
pp. 784
Author(s):  
Zhenxu Sun ◽  
Shuanbao Yao ◽  
Lianyi Wei ◽  
Yongfang Yao ◽  
Guowei Yang
Keyword(s):  
Drag Reduction ◽  
Pressure Distribution ◽  
Flow Separation ◽  
High Speed ◽  
Leeward Side ◽  
Detached Eddy Simulation ◽  
Side Force ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Asymmetrical Design

The structural design of the streamlined shape is the basis for high-speed train aerodynamic design. With use of the delayed detached-eddy simulation (DDES) method, the influence of four different structural types of the streamlined shape on aerodynamic performance and flow mechanism was investigated. These four designs were chosen elaborately, including a double-arch ellipsoid shape, a single-arch ellipsoid shape, a spindle shape with a front cowcatcher and a double-arch wide-flat shape. Two different running scenes, trains running in the open air or in crosswind conditions, were considered. Results reveal that when dealing with drag reduction of the whole train running in the open air, it needs to take into account how air resistance is distributed on both noses and then deal with them both rather than adjust only the head or the tail. An asymmetrical design is feasible with the head being a single-arch ellipsoid and the tail being a spindle with a front cowcatcher to achieve the minimum drag reduction. The single-arch ellipsoid design on both noses could aid in moderating the transverse amplitude of the side force on the tail resulting from the asymmetrical vortex structures in the flow field behind the tail. When crosswind is considered, the pressure distribution on the train surface becomes more disturbed, resulting in the increase of the side force and lift. The current study reveals that the double-arch wide-flat streamlined design helps to alleviate the side force and lift on both noses. The magnitude of side force on the head is 10 times as large as that on the tail while the lift on the head is slightly above that on the tail. Change of positions where flow separation takes place on the streamlined part is the main cause that leads to the opposite behaviors of pressure distribution on the head and on the tail. Under the influence of the ambient wind, flow separation occurs about distinct positions on the train surface and intricate vortices are generated at the leeward side, which add to the aerodynamic loads on the train in crosswind conditions. These results could help gain insight on choosing a most suitable streamlined shape under specific running conditions and acquiring a universal optimum nose shape as well.

The Aerodynamic Characteristics of the Pantograph When the Train Passes Through the Tunnel

2017 ◽  
Author(s):  
Dilong Guo ◽  
Wen Liu ◽  
Junhao Song ◽  
Ye Zhang ◽  
Guowei Yang
Keyword(s):  
High Speed ◽  
Aerodynamic Force ◽  
Maximum Amplitude ◽  
Aerodynamic Characteristics ◽  
High Speed Train ◽  
Expansion Waves ◽  
Compression And Expansion ◽  
High Speed Trains ◽  
Current Characteristics ◽  
Pass Through

The aerodynamic force acting on the pantograph by the airflow is obviously unsteady and has a certain vibration frequency and amplitude, while the high-speed train passes through the tunnel. In addition to the unsteady behavior in the open-air operation, the compressive and expansion waves in the tunnel will be generated due to the influence of the blocking ratio. The propagation of the compression and expansion waves in the tunnel will affect the pantograph pressure distribution and cause the pantograph stress state to change significantly, which affects the current characteristics of the pantograph. In this paper, the aerodynamic force of the pantograph is studied with the method of the IDDES combined with overset grid technique when high speed train passes through the tunnel. The results show that the aerodynamic force of the pantograph is subjected to violent oscillations when the pantograph passes through the tunnel, especially at the entrance of the tunnel, the exit of the tunnel and the expansion wave passing through the pantograph. The changes of the pantograph aerodynamic force can reach a maximum amplitude of 106%. When high-speed trains pass through tunnels at different speeds, the aerodynamic coefficients of the pantographs are roughly the same.

Sign in / Sign up

Export Citation Format

Share Document