Abstract:

Based on the single frame and single exposure imaging (SFSE) method for flow field measurement, the motion single frame and long exposure imaging (MSFLE) method is proposed for measuring the coherent structure of turbulence in the plant turbulent boundary layer. The method is a Lagrangian property measurement technique. The camera moves at substantially the same speed as the migration speed of the coherent structure, and the trajectory of the particle is recorded by the method of long exposure. Experiments were carried out with this method to measure the development of the coherent structure in the turbulent boundary layer. The evolution of the coherent structure with time and space were intuitively recorded. The motion characteristics of the coherent structure are analyzed. The experimental results show that the interaction between the high and low speed streaks can lead to the displacement, merging and dissipation of the hairpin vortex. The existence of stagnation point and strong shear layer is the key to the evolution of coherent structure.

Key words: turbulence, boundary layer, coherent structure, flow, image method, measurement

摘要：

在研究单帧单曝光图像法（SFSE）流场测量的基础上，提出了测量湍流边界层相干结构的运动单帧长曝光图像法（MSFLE），该方法是具有拉格朗日性质的测量方法，测量时相机以被拍摄相干结构的迁移速度基本相同的速度移动，同时采用长曝光的方法记录粒子的运动轨迹。应用该方法，得到了充分发展湍流边界层流向-展向平面内相干结构的直观图像，清晰地展示了相干结构随时间与空间的发展演变过程，并对其中的运动特征进行了分析研究。实验结果表明，高低速条带之间的相互作用可以导致发夹涡的位移、合并和耗散，鞍点及附近强剪切层的存在是相干结构发展演化的关键。

关键词: 湍流, 边界层, 相干结构, 流动, 图像法, 测量