Research On Aerodynamic Drag Reduction Of High-speed Train With Non-smooth Surface

As the train speed continuously improves, the interaction between the train and the air is gradually severe. Therefore aerodynamics of train has become a problem that can' t be neglected by us. When the train is at the speed of 300km/h, the air resistance contains about 85% of the total resistance. Thus, train' s air resistance is a major component of the total train resistance. Generally speaking, the air resistance of train is closely related to its shape and the proportion of it in the total resistance is also growing as the running speed increases. For this reason, the scientific community and industry focus on research and improve the aerodynamic characteristics of high-speed trains, reducing the aerodynamic drag of the high-speed trains to improve the energy utilization.Takes the maturing high-speed rail technology as research background the CHR2 high-speed train as research object, this paper applies non-smooth surface to the train's surface based on the research progress of non-smooth surface drag reduction and numerical simulation of the train in order to achieve better drag reduction effect.The models with 36 different kinds of non-smooth surfaces built using UG are divided into unstructured grids by using Hypermesh and ICEM CFD. Then, numerical simulation of flow characteristics of train' s external flow field is done when the mathematical model is at its steady state through Fluent. Also, this paper considers air drag coefficient as the assessment standard to the drag effects, analyses the impact of the non- smooth unit shape, spacing, diameter and depth of the drag reduction performance on reducing effects so as to smooth unit shape lay the foundation for the rational design of train surface of the non-smooth structure.Finally, this paper describes the effects of non-smooth surface on train' s external flowing field from different aspects by analyzing the composition of frictional resistance and pressure resistance. The causes of friction and pressure drag are explained by analyzing turbulent kinetic energy of different models and the pressure distribution of train' s surface. Besides, the drag reduction mechanism of non-smooth surface is further elaborated by studying non-smooth surface' s impact on boundary layer.