摘要
In this work,we study the development,evolution,and migration of turbulent coherent structures in the turbulent boundary layer at Reτ=630 using time-resolved particle image velocimetry(TR-PIV).Multiple techniques,including multi-scale analysis,conditional averaging,cross-correlation,and spatial-temporal topological analysis are applied to extract the evolution principle,migration trajectory,and convection velocity vector of the targeted coherent structures from a Lagrangian perspective.The spanwise vortex structures with larger scale and intensity at a certain wall-normal height y were the main focus of the present study.In the statistical sense,spanwise vortex structures move away from the wall with the shape changing from a bulge to an ellipse,and finally to a circle.Two straight lines emerge from the mean transfer trajectory curve of the spanwise vortex,in which the horizontal one is located at the viscous sublayer(y^(+)<10),the other is a logarithmic straight line existing in the range of 50<y^(+)<120,and the inclination angle of the tangential migration path is fixed at around 12°.The streamwise convection velocity U_(c)of scaled spanwise vortex structures satisfies U_(c)/U_(∞)=0.5-0.6 below y=0.03δ(i.e.,U^(+)_(c)=11-13 undery^(+)=20).In particular,in the region of 50<y^(+)<120,the velocity growth curves of U_(c)and wall-normal convection velocity V_(c)follow the log-law distribution very well,and the slopes are consistent with that of the log-law region of the turbulent boundary layer.Our observations provide microscopic evidences of the logarithmic-linear distribution of the migration trajectory of spanwise vortex structures.
使用时间分辨粒子图像测速仪(TR-PIV)研究了湍流边界层中湍流相干结构在Re_(τ)=630条件下的发展、演化和迁移.综合应用多尺度分析、条件平均、互相关和时空拓扑分析等技术,从拉格朗日视角提取目标相干结构的演化机理、迁移轨迹和对流速度矢量分布等规律.本研究重点关注位于壁面法向高度y.上具有较大尺度和强度的展向涡结构.统计结果显示:展向涡结构从壁面向外移动过程中,其形状从凸起变为椭圆,最后变为圆形.展向涡的迁移轨迹上呈现出两条直线,其中水平的一条位于黏性子层(y^(+)<10),另一条则是位于50<y^(+)<120范围内的对数直线,其与壁面的倾角固定在12°附近.在y=0.038以下位置,具有尺度特征的展向涡结构的流向对流速度U_(c)满足U_(c)/U_(∞)=0.5~0.6(即低于y^(+)=20时,U_(c)^(+)=11~13).在50<y^(+)<120区域,流向对流速度U_(c)和壁面法向对流速度V_(c)均很好地遵从了对数律分布,且斜率与湍流边界层对数律区的一致.本文的实验观测为展向涡结构迁移轨迹的对数线性分布提供了微观证据.
作者
Haiping Tian
Xingrui Yi
Fang Xi
Fen Li
Nan Jiang
田海平;伊兴睿;许放;李芬;姜楠(National Demonstration Center for Experimental Mechanics Education,Taiyuan University of Technology,Taiyuan 030024,China;Department of Mechanics and Aerospace Engineering,Southern University of Science and Technology,Shenzhen 518055,China;Department of Mechanics,Tianjin University,Tianjin 300350,China)
基金
the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.11802195)
the National Natural Science Foundation of China(Grant Nos.12172242,and 11972251)
the Key Program of the National Natural Science Foundation of China(Grant No.11732010)
Sino-German International Cooperation Project supported by Sino-German Science Center(GZ1575)
the Natural Science Foundation for Young Scientists of Shanxi Province,China(Grant No.201801D221027).
