Abstract The influence of ground clearance on the flow around a simplified high-speed train is investigated in this paper. Four clearance heights are studied using IDDES. After a grid independence study, the results of the simulations are validated against experimental data present in the literature. It is found that the drag decreases when reducing the clearance gap from the baseline height to a possibly critical height, while drag remains constant when the clearance is lower than this critical height. The negative lift (downforce) increases with the decreasing of the clearance gap. The flow is particularly influenced by the gap height at the underbody and wake regions, where a lower underbody velocity and a higher wake velocity are observed with lower clearance down to case h2. Therefore, the different topologies of the wake are presented and described. Particular attention is paid to the description of the wake flow and to the position and the formation of the flow mixing region. Specifically, with decreasing clearance, the mix of the tail downwash and underbody flows happen earlier, and the core of the counter-rotating vortices in the wake tends to develop with an increasing height trend. Overall, aerodynamic performance and flow structure descriptions show positive and negative effects when decreasing gap clearances, which should be taken into account for new design strategies.

中文翻译：

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离地间隙对普通高速列车空气动力学的影响

摘要 本文研究了离地间隙对简化高速列车周围流动的影响。使用 IDDES 研究了四个间隙高度。在进行网格独立性研究后，模拟结果将根据文献中的实验数据进行验证。发现当将间隙从基线高度减小到可能的临界高度时阻力减小，而当间隙低于该临界高度时阻力保持恒定。负升力（下压力）随着间隙的减小而增加。流动尤其受到底部和尾流区域的间隙高度的影响，在这种情况下，观察到较低的底部速度和较高的尾流速度，并且间隙较低，直到情况 h2。所以，介绍和描述了尾流的不同拓扑结构。特别注意尾流的描述以及流动混合区的位置和形成。具体而言，随着间隙的减小，尾部下洗流和底部流的混合发生得更早，尾流中的反向旋转涡流的核心趋于随着高度的增加而发展。总体而言，空气动力学性能和流动结构描述在减小间隙间隙时显示出正面和负面影响，新的设计策略应考虑到这一点。尾流中的逆旋涡核有高度增加的趋势。总的来说，空气动力学性能和流动结构描述在减小间隙间隙时显示出积极和消极的影响，新的设计策略应该考虑到这一点。尾流中的逆旋涡核有高度增加的趋势。总的来说，空气动力学性能和流动结构描述在减小间隙间隙时显示出积极和消极的影响，新的设计策略应该考虑到这一点。