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Evolution of the invariants of the velocity gradient tensor in the developing region of a round jet using tomographic PIV
Journal of Turbulence ( IF 1.9 ) Pub Date : 2021-07-27 , DOI: 10.1080/14685248.2021.1955121
Morteza Khashehchi 1 , Zambri Harun 2 , Yasser Mahmoudi Larimi 3
Affiliation  

Tomographic particle image velocimetry (Tomo-PIV) was performed to study the initial transition process formed in a free round jet between the laminar flow at the jet exit, and the fully turbulent flow region at Red = 6500. The evolution of the small-scale turbulence characteristics in this particular region has been assessed by means of the invariants of the velocity gradient tensor (VGT). These invariants enable us to study the dynamics, geometry, and topology of the turbulence phenomena. A mapping from the three-dimensional flow fields to a two-dimensional invariants plane is used to analyse the dissipation of kinetic energy at small-scales and the amplification of local vorticity due to vortex stretching. A systematic study of the event that represents the persistent alignment of the vorticity vector with the second eigenvector of the rate of strain tensor was examined, and the results of this phenomenon at the near-field of the jet are discussed. Results show that vorticity vector, ω, maintains its alignment with the intermediate eigenvector of the rate of strain tensor, υ2, in the developing region by either the rotation of the intermediate eigenframe or the tilting of ω.



中文翻译:

使用断层成像 PIV 的圆形射流发展区域速度梯度张量不变量的演化

进行断层扫描粒子图像测速 (Tomo-PIV) 以研究在射流出口处的层流与Re d处的完全湍流区域之间在自由圆形射流中形成的初始过渡过程 = 6500。这个特定区域的小尺度湍流特征的演变已经通过速度梯度张量 (VGT) 的不变量进行了评估。这些不变量使我们能够研究湍流现象的动力学、几何学和拓扑学。从三维流场到二维不变平面的映射用于分析小尺度动能的耗散和由于涡旋拉伸引起的局部涡量的放大。对代表涡量矢量与应变张量速率的第二特征矢量的持续对齐的事件进行了系统研究,并讨论了这种现象在射流近场的结果。结果表明,涡度矢量ω,通过中间特征框架的旋转或ω的倾斜,在发展区域中保持与应变张量速率的中间特征向量υ 2对齐。

更新日期:2021-09-30
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