Zhengwei Chen

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.