Effect of low operating temperature on the aerodynamic characteristics of a high-speed train

Abstract

In this study, an improved delayed detached eddy simulation (IDDES) method based on the shear-stress transport (SST) k-ω turbulence model has been used to investigate the underbody flow characteristics of a high-speed train operating at lower temperatures with Reynolds number Re =1.85×10^6. The accuracy of the numerical method has been validated by wind tunnel tests. The aerodynamic drag of the train, pressure distribution on the surface of the train, the flow around the vehicle, and the wake flow are compared for four temperature values: +15 °C, 0 °C, −15 °C, and −30 °C. It was found that lower operating temperatures significantly increased the aerodynamic drag force of the train. The drag overall at low temperatures increased by 5.3% (0 °C), 11.0% (−15 °C), and 17.4% (−30 °C), respectively, relative to the drag at +15 −C. In addition, the low temperature enhances the positive and negative pressures around and on the surface of the car body, raising the peak positive and negative pressure values in areas susceptible to impingement flow and to rapid changes in flow velocity. The range of train-induced winds around the car body is significantly reduced, the distribution area of vorticity moves backwards, and the airflow velocity in the bogie cavity is significantly increased. At the same time, the temperature causes a significant velocity reduction in the wake flow. It can be seen that the temperature reduction can seriously disturb the normal operation of the train while increasing the aerodynamic drag and energy consumption, and significantly interfering with the airflow characteristics around the car body. 目的 受空气物理参数变化影响,低温下列车周围的流场特性与常温时存在差异。本文旨在对高速列车在低运行温度下的空气动力学性能及流场特性变化研究予以补充,探究低温对列车周围流场、列车风及列车尾流等方面的影响,以提高高速列车的抗高寒性能。 创新点 1. 将气体参数设置为低温环境,探究列车相比常温下的气动性能及周围流场的变化。2. 对比不同低温环境,探究不同程度低温对列车气动特性的影响。 方法 1. 通过基于SST k-ω湍流模型的IDDES数值计算方法对高速列车在雷诺数约为1.85×106的条件下低温运行的流动特性进行仿真。2. 依托后处理软件对不同温度下列车气动阻力、表面压力分布、车身周围流动及尾流等进行分析。3. 将结果进行比对,得出不同程度低温对列车气动特性的影响。 结论 1. 低温显著增加列车气动阻力;相比常温环境,0 °C、−15 °C及∑30 °C时的气动阻力分别增加了5.3%、11.0%和17.4%。2. 低温会增强车体周围的正负压力场,进而提高冲击流及流速快速变化区域的正负压力峰值。3. 低温时,列车风的作用范围缩小,涡量分布区域后移,而转向架舱内的气流流速增加。4. 低温时,列车的尾流速度降低。