Tail Car Research Articles

Influences of marshalling length on the flow structure of a maglev train

In this paper, transient numerical simulations of maglev trains of different marshalling lengths (2, 4, and 8-car group trains) were conducted in the open air and without wind. This was done by solving the three-dimensional incompressible Navier-Stokes equations using an SST K-ω double-equation IDDES turbulence model. The results were compared with the results of wind tunnel experiments to verify the feasibility of numerical simulation. The results show an increase in the marshalling lengths of the train affects the flow above and below the train. With the increase of the marshalling length, the position of the flow separation in the tail car is advanced. The turbulence generated by the average shear on the x, y-plane and the x, z-plane as a component of the turbulence of the wake region increases. The region that produces non-vorticial vorticity in the main vortex becomes narrow and moves towards tail car. The structural analysis of the wake indicates that the wake structure of the 8-car group train is quite different from the other two groups. Both the time-averaged slipstream and the gust analysis show that the maximum expected slipstream velocity at the track-side increases as the train marshalling length increases. At the platform height, the change in vertical position of the wake vortex structure of the 2, 4, and 8-car group trains caused the difference of the shear flow regions. This is why the maximum expected slipstream velocity generated by the 4-car group train at this position is largest. As the marshalling length of the train increases, the time-average drag and lift force coefficient of the tail car have a significant negative correlation.

Aerodynamic Effects as a Maglev Train Passes Through a Noise Barrier

The aerodynamic performance of a maglev (magnetic levitation) train (MT) passing through a two-sided noise barrier was simulated by the improved delayed detached eddy simulations. The influence of the presence of noise barrier on both sides on the flow field around the MT and the pressure field in the noise barrier area are analyzed. The effect of changes of the noise barrier height and the centre of track (COT) distance parameter on its flow field were also studied. Numerical simulation results were verified by the moving model test. The results show that the noise barrier increases the pressure in the area around a train. The maximum pressure changes most as the tip of the head of the MT passes through the measuring point. The maximum positive and negative pressure amplitudes of the head wave on the inner wall surface of the noise barrier are increased by 83.5% and 58.4% compared to those the same height position measurement point in open air. On the inner wall of the barrier, the fluctuation of the pressure decreases with the increased height of the probe, which is opposite to the trend on the outer wall. Inside the noise barrier, the wind velocity in the x-direction is greater than that in open air when the tip of the nose and tail of the car passes. But the velocity in the y-direction when the tip of the head and tail cars passes is limited, and two speed peaks appear in the horizontal direction train induced wind. The higher the noise barrier, the higher pressure of the same height measurement point in the noise barrier area. Due to the passage of the train, the top of the noise barrier has a certain vorticity at the position of the head car and the tail car. Changing the height of the noise barrier changes how the vortex structure at the tail of the train develops. Moving the noise barrier further from the COT causes the fluctuations at the pressure measurement point inside the noise barrier to diminish meaning the pressure enhancement effect caused by the height of the noise barrier also diminishes.

Numerical investigation on the aerodynamics and dynamics of a high-speed train passing through a tornado-like vortex

This paper investigates the interaction between a high-speed train and a tornado-like vortex numerically using Detached Eddy Simulation and modal analysis. Key parameters related with the train operation safety, including the operation path, tornado intensity, and train speed, are considered. It is found that the train is subjected to larger aerodynamic forces and moments when the train operates along with the rotating vortex flow, and the head car is more dangerous comparing to the middle and tail cars. Coefficients of derailment and overturning are calculated with vehicle dynamics, and used to assess the operation safety of the train. It is also found that derailment is the main accident that might be caused by tornado, as the resultant lateral force acts at the lower half of the train. Moreover, resonant response of the train dynamic system to the aerodynamic loads caused by the tornado is observed. For the train and the dynamic parameters studied herein, the speed range for the occurrence of resonance is between 160km∕h and 250km∕h, within which the coefficients of derailment and overturning reach their maximum values. And the resonant phenomenon is independent with tornado intensity. The numerical results obtained in the current study are of significance for the assessment of operation safety while moving objects encountering tornadoes.

The influence of reduced cross-section on pressure transients from high-speed trains intersecting in a tunnel

Alleviation of the pressure transients caused by high-speed trains intersecting in a tunnel with partially reduced cross-section is investigated by numerical simulation. The RNG k-ε turbulence model and hybrid grid are adopted for the numerical simulation, which is validated by the moving model test. Two factors, the length of reduced section (L) and the train marshalling number, are considered to analyse the alleviation effect. The results show that, for reduction of the pressure transients induced by the intersection of three-car marshalling trains, the location of the change in cross-section is supposed to be near the location of the maximum value of the initial expansion wave (L → 240 ​m). In addition, for four-car marshalling trains intersecting in a tunnel of L ​= ​240 ​m, the excavation volume of the tunnel (tunnel volume) decreases by 14.4%, and the average pressure amplitude on the train surface decreases by 7.9%. Especially the pressure amplitude at the measurement point in the streamlined area of the tail car decreased by 28.6%. The reduced section tunnel has a good effect on decreasing the pressure transients around train body and the tunnel excavation volume (construction cost), which helps the tunnel design process.

Effect of Streamlined Nose Length on the Aerodynamic Performance of a 800 km/h Evacuated Tube Train

The aerodynamic resistance of a train running in the open air limits the maximum speed that can be attained by the train. For this reason, evacuated tube trains (ETT) are being considered as valid alternatives to be implemented in the future. The atmosphere in the tube, the so-called blocking ratio and the length of the streamlined nose are the key factors affecting the aerodynamic performances of these trains. In the present work, we investigate evacuated tube trains with different lengths of the streamline nose on the basis of computational fluid dynamics (CFD). The three-dimensional steady compressible Navier-Stokes equations are solved. The running speed of the ETT is 800 km/h and the blocking ratio is 0.2. Results show that with the increase of the streamlined nose length, the aerodynamic drag and lift forces of the head car decrease gradually, and the drag and lift forces of the middle car change slightly. For the tail car, the drag force decreases, whereas the absolute value of the lift force increases. At a speed of 800 km/h, a slight shock wave appears at the rear of the tail car, which affects the aerodynamic forces acting on the train.

Comparison of different configurations of aerodynamic braking plate on the flow around a high-speed train

End of vehicle streamlined head was selected as the installation location, and aerodynamic behavior of trains with and without braking plates was compared to analyze the formation of the braking force and the evolution of the flow field. An IDDES method based on the SST κ–ω turbulence model was used to investigate the unsteady flow, and the numerical algorithm was validated. Results show that the train aerodynamic drag was significantly increased by opening the braking plates, especially when several braking plates were arranged separately in series on each train car. Furthermore, the effect of the plate installed on the tail car was superior to that of the braking plate on the head car, when only a single braking plate was used. It was also found that both the maximum value of the slipstream and negative pressure close to the braking plate depend on the position and size of the braking plate. The flow field around the lower part of the train was only slightly affected by opening the braking plates, and pairs of vortices over the train appeared when the braking plates were opened, significantly affected both size and position of vortices in the train wake.

Aerodynamic effects of the gap spacing between adjacent vehicles on wind tunnel train models

A certain gap spacing between adjacent vehicles is usually inevitable in wind tunnel force tests of high-speed trains under no crosswind, which may affect the wind tunnel test results. Thus, to understand the influence of gap spacings on the train aerodynamics, the aerodynamic drag, pressure distributions and airflow structures of 1/8th-scale high-speed train models with gap spacings of 0, 5, 8, 10, 20, and 30 mm were studied using RANS based on SST k-ω turbulence model. The simulation method was verified by the wind tunnel experiment data. The results show that the gap spacing significantly affects the airflow structure around inter-car gap and aerodynamic resistances of train models. For the high-speed train model scaled at 1/8th at zero yaw, compared with gap spacing of 0 mm, the gap spacings lead to a significant reduction in the aerodynamic drag of the head car and an increase in that of the tail car, whereas which of the middle car is not significant. The maximum difference of the drag coefficient of the entire train model is smaller than 2.0%. When the gap spacing does not exceed 8 mm, the discrepancies of the drag coefficients of three cars are within 6.15%.

The use of non-smooth surfaces to control the wake of a high speed train

To solve some problems caused by the wake of a high-speed train, the control process, especially the mechanism of the non-smooth surface for controlling the wake of a high-speed train, is studied by using the detached eddy simulation. The numerical simulation method is validated by using the data from a wind tunnel experiment reported in literature. To study the passive control of the wake, the non-smooth surface is arranged on the front surface and the side surface of the train, respectively. The changes of the vortex structure, velocity, and aerodynamic drag before and after the control are presented, and then the flow control mechanism of the non-smooth surface is explored in detail. The results show that by arranging the non-smooth surface on the front and side surface of the tail car, the vortex motion in the tail of the train can be slowed down and the influence region of the wake can be shortened. At the same time, the velocity fluctuation amplitude in the wake region of the train apparently decreases and the aerodynamic drag of the train decreases after the control.

Numerical simulation and comparison of the slipstreams of trains with different nose lengths under crosswind

The slipstreams induced by high-speed trains under crosswind are studied in this paper by the detached-eddy simulation (DES) method. First, the formation and development of the slipstream induced by a train (5 cars) with a 4 m nose length are analysed in detail, including at different heights and widths on the windward side (WWS) and leeward side (LWS). Then, the slipstreams with and without crosswind are compared, and the differences are presented. Finally, by considering four different nose lengths (4, 7, 9, and 12 m) under crosswind, the differences in the slipstreams induced by different nose lengths are given and analysed. The results show that on the WWS at z = 0.5 m above the top of the rail (TOR), the slipstream velocity coefficient ‘U’ decreases at the position of the nose due to a velocity cancellation and stagnation effect. On the LWS, from D = 0 m–145 m, where ‘D’ represents the distance from the nose point, at y = 1.9 m and 2.15 m beside the centre of rail (COR), there are two peak values at the position of the nose caused by the impact of the nose point and the strong disturbance of the bogie area. At y = 2.65 m and 3.65 m, the change in U is relatively complex due to the effect of vortexes on the LWS. The effect of crosswind on the slipstream velocity is different in different regions around the train. In the region close to the train side and the bottom, the value of U on the WWS is the smallest, followed by that in the no wind case, and that on the LWS is the largest. In other regions, the values of U on the WWS and LWS are larger than that in the no wind case. For different nose lengths, on the WWS, the change in U is smoother with increasing nose length due to more stable flow around the nose. On the LWS, the change in U with increasing nose length is relatively clear only at the positions around the nose of the head car and tail car. In the regions along the middle cars, the U values for trains with different nose lengths change with the same trends and vary intertwined.

Effect of the outer windshield schemes on aerodynamic characteristics around the car-connecting parts and train aerodynamic performance

Abstract With the increasing speed of passenger trains, the train aerodynamics has deteriorated significantly. Abnormal vibration of windshield of the high-speed train occurred in the test of raising train speed to 350 km/h. To improve the design of a windshield with better aerodynamic performance, the aerodynamic performance of a high-speed train running at a speed of 350 km/h, especially the flow field around the windshields with six configurations, was investigated by numerical simulation and full-scale testing. The results show that the drag of the head car and tail car, and the lift force of the tail car are decreased by the most modified windshields, and the lift force of the head car is increased by the most modified windshields. Fluctuations of the drag and lift force of the tail car are reduced and increased by the modified windshields, respectively, and the effect of modified windshield on the fluctuation of the head car is confused. Vibration of the outer windshield is not suppressed, and even intensified by the modified windshields, and has no obvious relationship with windshield structure.

Optimization of the high-speed train head using the radial basis function morphing method

Aerodynamic drag reduction is one of the most important issues in the development of high-speed trains. This study focused on the aerodynamic optimization of the train by modifying the shape of the head car and tail car. Three shape parameters were studied in this paper: the angle of cab-window, nose-length, and nose-width of the train. The effects of shape parameters on the aerodynamic drag coefficients of the head car and tail car were discussed, respectively. It can be concluded that the flat surface of the window region, long and sharp nose are the distinguishing characters of a high-speed train with low resistance. Response surface models of the shape parameters and the aerodynamic drag of the head car and tail car were obtained, respectively. Based on these models, an aerodynamic optimization was performed to achieve the optimal shape. As a result, the total aerodynamic drag of the optimal train decreased by 2.05% compared with the original value.

Risks of Ear Complaints of Passengers and Drivers While Trains Are Passing Through Tunnels at High Speed: A Numerical Simulation and Experimental Study.

Ear complaints induced by interior pressure transients are common experiences for passengers and crew members when high-speed trains are passing through tunnels. However, approaches to assessing the risks of the pressure-related aural discomfort have not been reported until recently. The objective of this study was to evaluate the hazards of interior pressure transients of high-speed train on human ears combining the effects of operation speed and seal index. Moving model tests were conducted to obtain the pressure transients when the model train runs in the tunnel. The recorded data were transformed into the interior pressures by empirical formula. Furthermore, the aural sensations were divided into four levels hierarchically and the range for each level was derived by logistic regression analysis method and represented by three biomechanical metrics. Furthermore, a human middle ear finite element (FE) model was used to simulate its dynamics under the interior pressures. The results indicate that lifting operation speed from 250 km/h to 350 km/h in tunnel will prolong the duration of ear complaints by more than two times whereas improving the seal index from 4 s to 12 s will reduce the incidences of the onset of tinnitus and hearing loss by more than ten times. In addition, the duration of aural comfort shortens from the head car to the tail car against the running direction. It is desirable that enhancing the seal index improve the aural sensations of the passengers and crew members considering the lifting operation speed of high-speed train.

Numerical comparison of aerodynamic performance of stationary and moving trains with or without windbreak wall under crosswind

The aerodynamic performance of stationary and moving CRH2c trains with or without a windbreak wall under crosswind was simulated by DDES based on the SST κ-ω turbulence model. In this paper we present a comparison between the pressure on and around the trains, velocity around the trains, and the forces experienced by trains. Our work is an attempt to understand the difference in the aerodynamic performance between stationary and moving trains with or without a windbreak wall under crosswind. In addition, our study aims to determine whether the method applicable to stationary trains could replace that for moving trains. The numerical algorithm used in this simulation is verified by comparing its results with those obtained in a wind tunnel test. The results show that for a train without a windbreak wall under crosswind, the method for stationary trains can replace that for moving trains to simulate the pressure field around and the aerodynamic forces of a train, although the results may be relatively conservative. Furthermore, the aerodynamic forces of the tail car are almost insensitive to the train motion; however, for the simulation of the velocity field around the train, replacement of the method for moving trains by that for stationary trains requires careful consideration. The results showed that, for a train with a windbreak wall under crosswind, the method for moving trains cannot be replaced by that for stationary trains because the new vortices that are produced close to the body of the train by the windbreak wall are significantly affected by the motion of the train.

Performance of a turbine driven by train-induced wind in a tunnel

A simulation of the turbine driven by a high-speed train-induced wind in the tunnel was performed using the IDDES method with the SST k-w turbulence model. A full-scale real train experiment was conducted, and the results from a previously published study were employed to verify the computational method and mesh used for the simulation of the flow fields around the train and the turbine. The results show that the differences between the experiment and simulation results are very small. Next, certain variations of the torque of the turbine, the vorticity, velocity, pressure and specific dissipation rate of the flow field around the turbine during the process of the train crossing a tunnel are analysed. The obtained results show that not only the wake of the tail car but also the flow around the head car exerts great influence on the turbine. Next, a series of comparative studies were performed. The relationship between the maximum torque of the turbine and the distances from the turbine to the entrance and the exit of the tunnel, which can be modelled as power functions, were proposed. It was observed that while the maximum torque of the turbine decreases when the length of a tunnel varies from 100 to 300 m, it increases with the increasing length of the tunnel for lengths between 300 and 800 m.

Numerical analysis of aerodynamic characteristics of high-speed train with different train nose lengths

In this study, based on the SST κ-ω turbulent model, the IDDES method is used to simulate the unsteady aerodynamic performance of trains with respect to different lengths of the tapered nose of the train (8 m and 12 m). The numerical simulation used in this study is verified through wind tunnel tests. The effects of the length of the tapered nose of the train on the aerodynamic performance, such as the train forces, boundary layer, velocity distribution, pressure distribution, and flow structure around the train, are elucidated via comparing and analyzing the obtained results. The results indicate that the effect of the length of the tapered nose of the train on the drag force of the tail car and lift force of the head car is stronger than the effect on other cars, and the Cd value of the tail car decreases by 30.53% and the Cl value of the head car increases by 87.98%. Increase in the length of the tapered nose of the train decreases the fluctuation of the drag and lift forces of the train, especially the head car. It is also observed that the boundary layer thickness around the train is decreased with the increase in the length of the tapered nose of the train. Moreover, it is observed that vortex drag is the primary factor in the aerodynamic drag of the tail car and that vortex drag primarily depends on the length of the tapered nose of the train.

A novel $$\hbox {CACO}_{\mathrm{R}}$$ CACO R -SVR multi-objective optimization approach and its application in aerodynamic shape optimization of high-speed train

A chaos ant colony optimization algorithm for continuous domain is proposed based on chaos optimization theory and ant colony optimization algorithm. The searching abilities of optimization algorithms with different coding methods are compared, and the results indicate that the proposed algorithm has better performance than genetic algorithm and particle swarm optimization algorithm. Based on the non-dominated sorting concept and niching method, a multi-objective chaos ant colony optimization algorithm is also constructed and numerical results show that the improved algorithm performs well at solving multi-objective optimization problems. An optimal support vector regression model based on radial basis kernel function is developed for the small sample size and nonlinear characteristics of streamlined head optimization. On the basis of the above work, a multi-objective optimization design for the aerodynamic head shape of high-speed train is developed using a modified vehicle modeling function parametric approach. The optimization results demonstrate that the new optimization design method has exceptional searching abilities and high prediction accuracy. After optimization, the aerodynamic drag of the simplified train with three carriages is reduced by 10.52% and the aerodynamic lift of the tail car is reduced by 35.70%. The optimization approach proposed in the present paper is simple yet efficient and sheds light on the engineering design of aerodynamic shape of high-speed trains.

Comparative analysis of the effect of different nose lengths on train aerodynamic performance under crosswind

This study investigated the aerodynamic performances of four trains with different nose lengths (4, 7, 9 and 12 m) under strong crosswind using the detached eddy simulation (DES) method. The variations in the aerodynamic force coefficients with different nose lengths were analyzed. The pressure distribution on the train surface, vortex development around the train, and velocity field variation around the train with increases in the nose length were compared and discussed. The results indicated that in a strong wind environment, the aerodynamic drag coefficient was largest for the tail car, whereas the side force coefficient, lift coefficient and roll moment coefficient were largest for the head car. When the nose length of the train increased from 4 m to 12 m, the total drag coefficient of the train decreased by 19.0% and the side force, lift and roll moment coefficient decreased by 10.6%, 21.7% and 7.3%, respectively. In the horizontal section of the train head part and tail part, the largest pressure coefficient decreased in a logarithmic manner with increases in the nose length. The nose length significantly affects the pressure coefficient on the windward side of the head car and the leeward side of the tail car. With an increase in the nose length, on the leeward side of the train, the shedding length and influence width range of vortex were reduced; the strength of the spiral shedding and interaction effect of two vortices in the rear nose weakened, and their distinction was more notable, meanwhile, the wake impact ranges in the vertical and longitudinal directions decreased.

Numerical calculation of boundary layers and wake characteristics of high-speed trains with different lengths.

Trains with different numbers of cars running in the open air were simulated using the delayed detached-eddy simulation (DDES). The numbers of cars included in the simulation are 3, 4, 5 and 8. The aim of this study was to investigate how train length influences the boundary layer, the wake flow, the surface pressure, the aerodynamic drag and the friction drag. To certify the accuracy of the mesh and methods, the drag coefficients from numerical simulation of trains with 3 cars were compared with those from the wind tunnel test, and agreement was obtained. The results show that the boundary layer is thicker and the wake vortices are less symmetric as the train length increases. As a result, train length greatly affects pressure. The upper surface pressure of the tail car reduced by 2.9%, the side surface pressure of the tail car reduced by 8.3% and the underneath surface pressure of the tail car reduced by 19.7% in trains that included 3 cars to those including 8 cars. In addition, train length also has a significant effect on the friction drag coefficient and the drag coefficient. The friction drag coefficient of each car in a configuration decreases along the length of the train. In a comparison between trains consisting of 3 cars to those consisting of 8 cars, the friction drag coefficient of the tail car reduced by 8.6% and the drag coefficient of the tail car reduced by 3.7%.

Study on Distribution Characteristics of Aerodynamic Drag of a Couple Multiple Units High-Speed Train

Based on unsteady N-S equation of three-dimensional and compressible viscous fluid, the transient pressure on the car surface, both the flow structures and aerodynamic loads are analyzed in detail, the contribution value of all regions of a couple multiple units high-speed train for aerodynamic drag coefficient of the CRH2 whole train is studied. The calculation result shows that by contrasting the results of wind tunnel test with numerical simulation respectively using indirect verification method, the change law of aerodynamic effect shows agreeable accordance with the error under 5%. The aerodynamic drag of head surface area of the front and tail car and the bogie region of each car accounts for 75％ of the whole train. The aerodynamic drag coefficient of the later head surface area is twice more than the head surface area in the multiple units region. From the head

Study on the Aerodynamic Performance of the High-Speed Train Head with Symmetrical and Asymmetric Nose Shape

This study focused on the use of mesh morphing on optimizing high-speed train shape. Three shape variables were studied in this paper: the angle of cab-window, length of train-nose and width of train-nose. The original high-speed train head was optimized in symmetrical and asymmetric deformation. Total drag coefficient and lift coefficient of head car and tail car were optimized using Kriging model and NSGA- Ⅱ. As a result, three objective aerodynamic performance of the optimal train in symmetrical deformation is slightly improved comparing with the original ones and that in asymmetric deformation is improved significantly. Also, results of the symmetrical and asymmetric optimized high-speed train running in different speed were compared with that of the original high-speed train. Proposed method in this paper has been proved to be an efficient and feasible approach to study and optimize the aerodynamic performance of different high-speed trains as well as other structures.