Tanghong Liu

Numerical simulation of aerodynamic performance of a couple multiple units high-speed train

ABSTRACT In order to determine the effect of the coupling region on train aerodynamic performance, and how the coupling region affects aerodynamic performance of the couple multiple units trains when they both run and pass each other in open air, the entrance of two such trains into a tunnel and their passing each other in the tunnel was simulated in Fluent 14.0. The numerical algorithm employed in this study was verified by the data of scaled and full-scale train tests, and the difference lies within an acceptable range. The results demonstrate that the distribution of aerodynamic forces on the train cars is altered by the coupling region; however, the coupling region has marginal effect on the drag and lateral force on the whole train under crosswind, and the lateral force on the train cars is more sensitive to couple multiple units compared to the other two force coefficients. It is also determined that the component of the coupling region increases the fluctuation of aerodynamic coefficients for each train car under crosswind. Affected by the coupling region, a positive pressure pulse was introduced in the alternating pressure produced by trains passing by each other in the open air, and the amplitude of the alternating pressure was decreased by the coupling region. The amplitude of the alternating pressure on the train or on the tunnel was significantly decreased by the coupling region of the train. This phenomenon did not alter the distribution law of pressure on the train and tunnel; moreover, the effect of the coupling region on trains passing by each other in the tunnel is stronger than that on a single train passing through the tunnel.

Aerodynamic Effects Caused by Trains Entering Tunnels

With the increase in train speed, the aerodynamics in tunnels is emerging. In recent years, we have carried out a few full-scale tests about tunnel aerodynamics, and the law of influence of train speed on pressure change, airflow velocity, and micropressure wave are obtained, and a passenger comfort survey was conducted. When a high-speed train enters a tunnel at 200 km/h, the pressure change amplitude and pressure change per second inside the vehicle are 1,036 Pa and 273 Pa/s, respectively, and 88.9% people experienced no obvious discomfort; the airflow velocity in the tunnel is 14.8 m/s, which exceeds the criterion, 14 m/s. Therefore, it is suggested that workers should not work in the tunnel when a train passes; because the micropressure wave is only 9.7 Pa at the measured point, 20 m from the exit port of tunnel, the tunnel has a cross section enlarged hood with windows, and the passing train does not impact the environment near the tunnel.

Aerodynamic analysis of trains with different streamlined lengths of heads

Aerodynamic analysis of trains in open air without crosswind was studied using the detached-eddy simulation (DES) method in the present work. Three kinds of train model, with different streamlined lengths of heads but the identical cross section and train length, were investigated. The streamlined lengths are 5m, 9m, and 15m, respectively. To find the influence of streamlined lengths on the aerodynamic properties, the drag coefficient, surface pressure, trackside pressure, slipstream velocity variation along the length of the train and the flow structures around the train, were compared and analyzed. The result of the total drag coefficient decreased 22.4% with the streamlined length increased from 5m to 15m. The longer streamlined length can reduce the strength of vortex shedding and wake flow effectively, and a minor positive pressure area was generated in the nose cone compared to shorter streamlined length.

A CFD analysis of the aerodynamics of a high-speed train passing through a windbreak transition under crosswind

ABSTRACT In areas with strong wind, windbreaks are built along railways to reduce the impact of wind on trains. However, because of the restrictions imposed by actual terrain, windbreak structures are often not uniform, such as from a cutting to an embankment, resulting in a discontinuous transition region. When a train runs through this region, a distinct yawing phenomenon occurs. This study numerically explored the aerodynamic features of a train running through a rectangular windbreak transition region. The variations in the pressure, side force, and moment of a train were analyzed, and the flow field features were clarified. Furthermore, the yawing motion of the car body with time was described. Finally, based on EN14067-6, the critical wind speed was obtained using the safety assessment of a train running through a windbreak transition region.

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

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 1.8u2009×u2009106, 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 2.5u2009m and the distance from the top of the rail is greater than 1.5u2009m, 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.

Effect of Cutting Slope Angle on Aerodynamic Performance of High-speed Trains

Research on aerodynamic performance of high-speed trains in cutting with different slope angles would complement the operation safety management under strong winds. This study was conducted to investigate the flow structure around train using computational fluid dynamics (CFD). The accuracy of the numerical method was validated, combined with wind tunnel test. This work shows that the surroundings of cutting along the railway line have great effect on the crosswind stability of train. With the increase of slope angle , the coefficients of aerodynamic forces tend to reduce. Comparing the angle 0° with 90°, the Cs, Cl and Cm of head car fall by 96.7%, 108%, and 96.8% to the maximum respectively, while those of middle car by 108%, 98.8%, and 105%. For the shield of applicable cutting, the whole body is in a minor positive pressure environment. Thus, an appropriate slope angle for the cutting can largely improve its windbreak performance.