升力翼对高速列车列车风与尾流特性的影响

Effect of lift airfoils on characteristics of slipstream and wake flow of high-speed trains

为探究在高速列车车顶安装升力翼后引起的列车周围流场剧变,以三车编组1∶10缩尺比某型CRH高速列车模型为研究对象,采用基于两方程湍流模型的改进型延迟分离涡模拟(IDDES)方法,对比分析了有无升力翼的2种高速列车时均和瞬时列车风的发展规律;利用涡旋识别方法探讨了尾迹区瞬时涡结构分布特征,通过比较尾迹区不同流向位置的列车风分布特征与尾流涡旋移动规律,验证了列车风速度峰值与尾涡非定常特性的相关性,采用频谱分析方法获得了尾迹区速度功率谱密度曲线。研究结果表明:升力翼的几何外形结构加剧了车身表面边界层分离,令列车顶部和侧表面边界层厚度增大;升力翼使列车风速度峰值增大,其中在轨侧和站台位置最大时均列车风速度分别增大了1.556和1.327倍,且相较原型列车第2个峰值位置延后;由于翼尖涡不断向下游发展和累积,升力翼列车尾流结构表现为大尺度涡对中夹杂着一对更为破碎的细小涡旋,相较原型列车,涡旋与地面之间的剪切作用更强,升力翼列车尾流时均列车风速度在展向分布上有所增大,但垂直分布上有所降低,并在水平面上出现更明显的剪切分离;升力翼列车尾迹中包含较多破碎的小尺度涡,进而影响了尾迹涡脱落频率,使之比原型列车具有更高的能量,且涡旋耗散速度更慢。

A 1∶10 three-car CRH high-speed train model was taken as the research object to explore the drastic change of the flow field around the high-speed train caused by the installation of lift airfoils on the roof.An improved delayed detached eddy simulation(IDDES)method based on the two-equation turbulence model was adopted to analyze the development tendencies of the time-averaged and instantaneous slipstreams of two high-speed trains with and without lift airfoils.The distribution characteristics of instantaneous vortex structures in the wake region were discussed by a vortex identification method.The correlation between the peak slipstream velocity and unsteady characteristics of wake vortices was verified by the comparison of the slipstream distribution characteristics at different flow positions in the wake region and the movement laws of wake vortices.The power spectrum density curves of the velocity in the wake region were obtained by means of the spectral analysis.Research results show that due to the geometric structure of lift airfoils,the boundary layer separation on the train surface is intensified,and the thicknesses of the boundary layers on the roof and side surfaces of the train increase.The peak slipstream velocity is raised by the lift airfoils.Specifically,the maximum time-averaged slipstream velocities at the trackside and platform position increase by 1.556 and 1.327 times,respectively.It is delayed compared with the second peak position of the traditional train.Due to the continuous development and accumulation of wing-tip vortices downstream,the wake flow structure of the train with lift airfoils is manifested as a large-scale vortex pair mixed with a pair of more broken small vortices.Compared with the traditional train,the shear effect between the vortex and the ground is stronger,the time-averaged slipstream velocity of the wake flow of the train with lift airfoils is larger in the spanwise distribution but smaller in the vertical distribution.Moreover,there is a more obvious shear separation on the horizontal plane.Many small-scale broken vortices are incorporated in the wake of the train with lift airfoils,affecting the shedding frequency of vortices in the wake.As a result,compared with the traditional train,the train with lift airfoils has higher energy and slower vortex dissipation velocity.