剪切水-气界面下湍流猝发特征的实验研究

利用氢气泡时间线-脉线组合示踪技术定量地考察剪切水-气界面下的湍流猝发现象，分析 猝发事件的信号特征，重点探讨猝发与湍能产生之间的联系. 在猝发过程中，水面近区的瞬 时流速和Reynolds切应力出现较大幅度的脉动，它们在时间和空间垂直方向上表现出高度 的相干性，这是猝发事件的一个显著特征. 在猝发期，猝发事件涉及的空间区域内Reynolds 切应力和湍流脉动强度明显比平均值和非猝发期的情况大. 其结果表明：在所考察的实验 条件下，猝发是剪切水-气界面附近湍流产生的主要过程.

Experimental investigation of the bursting characteristics under sheared air-water interface

The bursting phenomenon under a sheared air-water interface is quantitatively examined using combined-time-streak markers of hydrogen bubbles. Based upon samples of instantaneous velocity profiles derived from flow visualization pictures, the signal characteristics of bursting event are analyzed, and particular emphasis is placed on the relation between bursting processes and the production of turbulence near air-water interface. During a bursting, the instantaneous velocities and Reynolds shear stress near air-water interface fluctuate in relatively large amplitude, which appear to be associated with the ejection phenomena of low-speed streak. Their high degree of coherence in time and in the vertical direction is the most notable characteristic of bursting event. In bursting times, the values of Reynolds shear stress and turbulence intensity rise considerably in the region where bursting phenomenon is observed, and become much higher than the mean value and that in non-bursting period. The present data establish, for the case studied, that bursting processes is the main contributor of turbulent kinetic energy near sheared air-water interface.