Hairpin vortices and highly elongated flow structures in a stably stratified shear layer
Hairpin vortices and highly elongated flow structures in a stably stratified shear layer
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DOI：
10.1017/jfm.2019.577
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发表时间：
2019-09
影响因子：
3.7
通讯作者：
Tomoaki Watanabe;J. Riley;K. Nagata;K. Matsuda;R. Onishi
中科院分区：
文献类型：
--
作者：
Tomoaki Watanabe;J. Riley;K. Nagata;K. Matsuda;R. Onishi
采用直接数值模拟方法研究了稳定层状剪切层中的湍流结构。流动显示证实了具有正、负速度脉动的发夹涡和高度拉长结构的存在，其流向长度除以层厚度分别为$O(10^{0})$和$O(10^{1})$。与这些结构相关的波长处的流动对湍动能有很大的贡献。这些结构在后期变得突出，但浮力雷诺数较小，表明湍流混合受到抑制。然而，与发夹涡旋相关的主动湍流混合确实发生了。整体剪切参数的结构和垂直剖面显示了稳定的层状剪切层和壁面剪切流之间的联系。
Turbulent structures in stably stratified shear layers are studied with direct numerical simulation. Flow visualization confirms the existence of hairpin vortices and highly elongated structures with positive and negative velocity fluctuations, whose streamwise lengths divided by the layer thickness are $O(10^{0})$ and $O(10^{1})$ , respectively. The flow at the wavelength related to these structures makes a large contribution to turbulent kinetic energy. These structures become prominent in late time, but with small buoyancy Reynolds numbers indicating suppression of turbulent mixing. Active turbulent mixing associated with the hairpin vortices, however, does occur. The structures and the vertical profile of the integral shear parameter show connections between stable stratified shear layers and wall-bounded shear flows.