Compressibility effects on statistics and coherent structures of compressible turbulent mixing layers
Compressibility effects on statistics and coherent structures of compressible turbulent mixing layers
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可压缩性对可压缩湍流混合层统计和相干结构的影响
DOI：
10.1017/jfm.2022.660
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发表时间：
2022-08
影响因子：
3.7
通讯作者：
Shiyi Chen
中科院分区：
文献类型：
--
作者：
Xiaoning Wang;Jianchun Wang;Shiyi Chen
本文用数值模拟的方法研究了对流马赫数为0.2 ~ 1.8和泰勒雷诺数为290时，压缩性对混合层统计特性和相干结构的影响。随着对流马赫数的增加，流向耗散对湍流动能的抑制作用增强。在$M_c=1.8$时，流向耗散的增长速度远快于其他两个分量，甚至大于压力-应变重分布，这与高压缩性下流向细长涡结构有关。我们证实了混合层中存在大规模的高速和低速结构，在低对流马赫数下，这些结构伴随着展向Kelvin-Helmholtz滚子，在高对流马赫数下，这些结构在混合层中占主导地位。有条件的统计表明，大型低速结构物被一对反向旋转的准流向辊两侧的结构向上提升。小尺度涡结构有明显的倾向于聚集到低速区的顶部，这是直接相关的高速剪切运动的顶部的低速结构。高速结构与低速结构在统计上表现出中心对称性。可压缩混合层中大尺度高、低速结构的统计和动力学特征与湍流边界层外区相似，揭示了自由剪切湍流和壁面湍流大尺度结构的普遍性。本文介绍了湍流混合层中大尺度高低速结构的概念模型。
The effects of compressibility on the statistics and coherent structures of a temporally developing mixing layer are studied using numerical simulations at convective Mach numbers ranging from $M_c=0.2$ to $1.8$ and at Taylor Reynolds numbers up to 290. As the convective Mach number increases, the streamwise dissipation becomes more effective to suppress the turbulent kinetic energy. At $M_c=1.8$ , the streamwise dissipation increases much faster than the other two components in the transition region, even larger than pressure–strain redistribution, correlating with the streamwise elongated vortical structures at a higher level of compressibility. We confirm the existence of the large-scale high- and low-speed structures in the mixing layers, which accompany the spanwise Kelvin–Helmholtz rollers at low convective Mach number and dominate the mixing layer at higher convective Mach number. Conditional statistics demonstrate that the large-scale low-speed structures are lifted upwards by a pair of counter-rotating quasi-streamwise rollers flanking the structures. The small-scale vortical structures have an apparent preference for clustering into the top of the low-speed regions, which is directly associated with high-shearing motions on top of the low-speed structures. The high-speed structures statistically exhibit central symmetry with the low-speed structures. The statistics and dynamics of large-scale high- and low-speed structures in the compressible mixing layers resemble those in the outer region of the turbulent boundary layers, which reveals the universality of the large-scale structures in free shear and wall-bounded turbulence. A conceptual model is introduced for the large-scale high- and low-speed structures in turbulent mixing layers.
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