The crosswind is one of the factors that can lead to a car accident. Crosswind is defined as a side force that causes a vehicle to become unstable and deviate from its desired path. This article focuses on evaluating the flow behaviour and aerodynamic loads that affect vehicle stability when driving in a steady crosswind. In this study, a numerical approach is used with the ANSYS Fluent software as a platform to run the simulation. In this research, the crosswind flow angle (Ψ) is varied from 0° to 90°. The incompressible flow surrounding the vehicle is solved using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunctions with the k-ε turbulence model. The Reynolds number is utilized depending on the velocity of the vehicle which are 2.8×106 for high Reynolds number and 7.2×105 for low Reynolds number respectively. According to the findings, the crosswind has a significant quantitative and qualitative impact on aerodynamics. In terms of aerodynamic load, the side coefficient (Cs) increases as the crosswind yaw angle increases. When the crosswind yaw angle reaches 60°, there is a significant drop, but it remains almost constant when the crosswind yaw angle reaches 90°. In terms of flow structure, as the crosswind yaw angle increases, the vortex formation on the leeward region expands, increasing the vehicle stability imbalance. Finally, there is no significant difference in the quantitative aerodynamic characteristics of high and low Reynolds numbers.
Improvement to the next-generation high-speed train (NG-HST) is ongoing particularly in achieving a higher operating speed. Consequently, the aerodynamic effect of the train will be more critical as it affects the development of a wake flow characterized by complex and unsteady structures. Although the effect of Reynolds number (Re) on aerodynamic forces is negligible, its effect on the wake of NG-HSTs is unknown. In this study, the Re ranging from 7.42 × 105 to 1.62 × 106 was used to examine the characteristics of vortex structures, streamline distributions, velocity characteristics, and pressure characteristics in the wake region of an NG-HST. The Delayed Detached Eddy Simulation (DDES) is used as the turbulence model. In addition, the simulation results were compared with the previous wind tunnel experimental data. The results indicated no significant changes in the overall wake flow structure when Re was increased. According to power spectral density analysis, increasing the Reynolds number increased the turbulence intensity of the wake which gradually dissipated as the distance from the train increased. The findings of the study could be used to better understand the flow characteristics at the wake of NG-HSTs for future development.
The development of Next-Generation Trains (NGT) made of lightweight materials is a challenging task for the transport industry. It reduces axle loads, which saves money by lowering rail track maintenance costs and the amount of energy needed to drive vehicles. However, the increasing speed and decreasing mass of high-speed trains, on the other hand, raises concerns about the effects of strong crosswinds on their aerodynamics and train stability. As a result, the purpose of this research is to investigate the unsteady flow structure around an NGT in crosswind using a Computational Fluid Dynamics (CFD) technique known as Unsteady Reynolds Averaged Navier-Stokes (URANS). Based on the height of the train model and the velocity, the Reynolds number for the simulation used was . The simulation run in four different crosswind angles: 5°, 10°, 15°, and 20°. The simulation results were compared with experimental results. The findings revealed that a larger yaw angle, which is primarily determined by the incoming wind velocity, can lead to higher flow separation and a more complex three-dimensional flow around the train. Additionally, when the wind angle is small, separation of flow and wakes is limited to the train's end; however, as the wind angle increases, separation of flow occurs from the train's upper and lower corners, indicating that the vortices formed as a result of the flow passing over the roof top and underbody. Finally, the study's findings will contribute to a better understanding of the flow characteristics around an NGT in crosswinds, which is simply impossible to achieve through full-scale testing due to the cost, resources, and accuracy.
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