On the physical nature of the turbulent/turbulent interface
On the physical nature of the turbulent/turbulent interface
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关于湍流/湍流界面的物理性质
DOI：
10.1017/jfm.2022.388
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发表时间：
2022
影响因子：
3.7
通讯作者：
Kankanwadi K
中科院分区：
文献类型：
--
作者：
Kankanwadi K
湍流/湍流界面（TTI）的存在最近已经在暴露于自由流湍流的圆柱体的远尾流中得到验证（Kankanwadi & Buxton，J. Fluid Mech.，第905卷，2020年，第A35页）。本研究旨在了解TTI内的物理学。尾流边界，约40直径下游的圆柱受到网格产生的湍流，通过同步电影，立体粒子图像测速和平面激光诱导荧光实验进行了研究。在圆柱体上游没有放置网格的情况下，所得界面的行为，我们对湍流/非湍流界面的最接近近似，与现有文献中观察到的完全匹配。当背景湍流存在时，粘性作用不再是将拟能传递到背景流体的唯一方法，这与湍流/非湍流界面不同。TTI两侧的旋转流体的存在允许涡度拟能预算方程的涡度拉伸项在这个过程中占主导地位。当涡度拉伸项接管涡度拟能产生的责任时，TTI内粘性的作用大大减弱。垂直于TTI的湍流应变速率被发现在界面区域中被增强。将涡度拉伸项分解成与三个主要应变率方向一致的分量，发现与界面法线方向最一致的项贡献了涡度拟能产生的最大份额。这表明，界面尾流侧更好的“组织”涡度产生涡度拟能放大，导致Kankanwadi和Buxton先前发现的跨TTI的涡度拟能跳跃（J. Fluid Mech.，第905卷，2020年，第A35页）。
The existence of a turbulent/turbulent interface (TTI) has recently been verified in the far wake of a circular cylinder exposed to free-stream turbulence (Kankanwadi & Buxton, J. Fluid Mech., vol. 905, 2020, p. A35). This study aims to understand the physics within the TTI. The wake boundary, approximately 40 diameters downstream of a circular cylinder subjected to grid-generated turbulence, was investigated through simultaneous cinematographic, stereoscopic particle image velocimetry and planar laser induced fluorescence experiments. With no grid placed upstream of the cylinder, the behaviour of the resultant interface, our closest approximation to a turbulent/non-turbulent interface, exactly matched what is observed in existing literature. When background turbulence is present, viscous action is no longer the only method by which enstrophy is transported to the background fluid, unlike for turbulent/non-turbulent interfaces. The presence of rotational fluid on both sides of the TTI allows the vorticity stretching term of the enstrophy budget equation to be the dominant actor in this process. The role of viscosity within a TTI is greatly diminished as the vorticity stretching term takes over responsibilities for enstrophy production. The turbulent strain rate normal to the TTI was found to be enhanced in the interfacial region. Decomposing the vorticity stretching term into components aligned with the three principal strain-rate directions, it was found that the term most aligned with the interface-normal direction contributed to the largest share of enstrophy production. This indicates that better ‘organised’ vorticity on the wake side of the interface yields the enstrophy amplification leading to the previously discovered enstrophy jump across the TTI by Kankanwadi & Buxton (J. Fluid Mech., vol. 905, 2020, p. A35).
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