基于降阶模型的高速列车尾涡动力学演化特性及列车风形成机理研究

The wake of a high-speed train demonstrates complicated three-dimensional and unsteady turbulent nature, characterized by the intercoupling of multi-scale flow structures, including shear layer, vortex shedding, separation bubble and streamwise vortex pair. The tail train oscillation and slipstream induced by unsteady trailing vortices could seriously affect the stability and safety of train operation. However, the unsteady nature of the wake and the formation mechanism of the slipstream have not been clearly clarified. In this project, wind tunnel test and numerical simulation are both applied to obtain the unsteady wake flow field. Modal decomposition methods are utilized to extract the dominant flow modes or coherent structures of the wake. Then the reduced-order models are constructed to investigate the temporal and spatial evolution of topological structure of the three-dimensional wake and explore its correlation with the near-wake slipstream. In the meantime, the influence of Reynolds number, incoming turbulence intensity and train length on the turbulence characteristics are studied together to verify the sensitivity factors affecting the unsteadiness in the wake. In addition, the effect of the tail slant angle and side taper angle on the vortex dynamics of the three-dimensional topological structure of the wake and corresponding slipstream is examined to reveal the formation mechanism of the slipstream in the near wake for different tail shapes. This project has great scientific significance of understanding the complex unsteady wake pattern of high-speed train, as it can provide guidance for the shape design of a tail train, avoid the negative effects caused by the unsteady trailing vortex and improve the stability and safety of train operation, thus could find important application in railway industry.

高速列车尾迹呈现出复杂的三维非定常湍流特性，包含剪切层、涡脱落、分离泡以及流向涡对等多尺度流动结构的相互耦合。由非定常尾涡引起的尾摆和列车风严重影响列车运行的稳定和安全，然而三维尾涡的非定常特性及列车风形成机理仍未被清晰阐明。本项目采用风洞试验和数值仿真获取尾迹非定常流动信息，利用模态分解方法提取尾迹中主导的流动模态或相干结构，构建降阶模型，剖析三维尾涡拓扑结构随时间和空间的演化规律，探究其与近尾迹列车风的相关性；同时研究雷诺数、来流湍流度和编组长度对尾迹湍流特性的影响，探明尾部非定常流场研究的敏感性因素；通过尾部后倾角和侧面收缩角对三维尾涡拓扑结构及其动力学特性和列车风的影响研究，揭示不同尾部形状的近尾迹列车风的形成机理。本项目对于理解湍流尾迹的复杂非定常流动结构具有重要科学意义，可用于指导设计列车尾部形状，避免非定常尾涡引起的负面作用，提高列车运行的稳定和安全性，具有重要实际应用价值。

高速列车尾迹呈现出复杂的三维非定常湍流特性，包含剪切层、涡脱落、分离泡以及流向涡对等多尺度流动结构的相互耦合。随着高速列车速度的不断提升，列车尾部非定常尾迹引起的列车风安全问题越来越凸显。而目前三维尾涡的动力学演化特性及关键影响因素尚不明确，且其与近尾迹列车风峰值的相关性还未被完全建立。本项目采用IDDES非定常数值模拟、风洞实验和谱本征正交分解SPOD方法相结合，重点研究转向架构型、来流湍流、雷诺数效应、编组长度以及尾部形状等关键因素对列车气动特性、三维非定常尾涡及列车风的影响。首先，阐明了基于SPOD和DMD等模态分解的降阶模型方法在三维湍流尾迹中的适用性，并将SPOD成功用于高速列车三维尾迹速度场的降阶及重构，建立了非定常尾涡动力学特性与近尾迹列车风峰值之间的关联，并揭示了转向架区域带来的底部扰动对流向涡对不稳定性及列车风的重要影响；其次，研究发现来流湍流是影响列车气动特性及非定常尾迹的更为关键的因素，重点阐明了湍流度和积分尺度对列车气动力、三维尾涡拓扑结构和列车风的影响规律及作用机制；同时也明确了雷诺数效应和编组长度对尾涡和列车风的影响；最后，探明了尾部后倾角和侧面收缩角对气动力、三维尾涡拓扑结构及列车风的影响，确认了高速列车尾涡拓扑结构发生改变的典型尾部形状，建立了列车尾部形状、三维尾涡动力学演化特性和近尾迹列车风三者的相关性。综上，本项目对于理解高速列车三维湍流尾迹的复杂流动结构和列车风形成机制具有重要科学意义，可用于指导设计合理的列车尾部形状，最大限度地减弱非定常尾涡引起的负面作用，提高列车运行的稳定性、安全性和经济性，为我国“一带一路”和高铁“走出去”国家战略的实施，提供空气动力学方面的相关理论支撑。