Amplification of enstrophy in the far field of an axisymmetric turbulent jet
Amplification of enstrophy in the far field of an axisymmetric turbulent jet
复制标题
DOI：
10.1017/s0022112009993892
复制
发表时间：
2010-05-25
影响因子：
3.7
通讯作者：
Ganapathisubramani, B.
中科院分区：
文献类型：
--
作者：
Buxton, O. R. H.;Ganapathisubramani, B.
利用电影立体粒子图像测速数据探讨了拟能的放大。涡度拟能产生率是通过观察涡度矢量（ω）与应变张量率（e（1））的特征向量的统计趋势来研究的。之前的研究表明，欧米茄优先与中间应变率特征向量（e（2））对齐，并且与广泛应变率特征向量（e（1））任意对齐。然而，这项研究表明，拟能放大的性质，无论是正的（拟能产生）还是负的（拟能破坏），都是由ω和e（1）之间的对齐决定的。平行排列导致拟能产生（ω S-i（ii）ω（i）> 0），而垂直排列导致拟能破坏（ω S-i（ii）ω（i）< 0）。这样，ω和e（1）之间的任意排列是涡度拟能产生区域和涡度拟能破坏区域的影响的总和。涡度拟能产生的结构也与中间应变率本征值s（2）有关。涡度拟能产生区被发现是拓扑“片状”，由于在这些地区的广泛（正）值的s（2），而涡度拟能破坏区被发现是“斑点”。强涡度拟能产生区出现在强局部涡旋区和高耗散区。瞬时可视化，从泰勒的假设所创建的数据量产生的，揭示了这些“片状”强拟能产生区域包括高拟能，强烈旋转的“蠕虫”。这些'蠕虫'诱导高的本地应变场导致形成的耗散'片'，从而揭示拟能生产是一个复杂的相互作用之间的旋转和应变的斜对称和对称分量的速度梯度张量，分别。
The amplification of enstrophy is explored using cinematographic stereoscopic particle image velocimetry data. The enstrophy production rate is investigated by observation of the statistical tendency of the vorticity vector (omega) to align with the eigenvectors of the rate of strain tensor (e(1)). Previous studies have shown that omega preferentially aligns with the intermediate strain-rate eigenvector (e(2)) and is arbitrarily aligned with the extensive strain-rate eigenvector (e(1)). This study shows, however, that the nature of enstrophy amplification, whether it is positive (enstrophy production) or negative (enstrophy destruction), is dictated by the alignment between omega and e(1). Parallel alignment leads to enstrophy production (omega S-i(ii)omega(i) > 0), whereas perpendicular alignment leads to enstrophy destruction (omega S-i(ii)omega(i) < 0). In this way, the arbitrary alignment between omega and e(1) is the summation of the effects of enstrophy producing and enstrophy destroying regions. The structure of enstrophy production is also examined with regards to the intermediate strain-rate eigenvalue, s(2). Enstrophy producing regions are found to be topologically 'sheet-forming', due to an extensive (positive) value of s(2) in these regions, whereas enstrophy destroying regions are found to be 'spotty'. Strong enstrophy producing regions are observed to occur in areas of strong local swirling as well as in highly dissipative regions. Instantaneous visualizations, produced from the volume of data created by Taylor's hypothesis, reveal that these 'sheet-like' strong enstrophy producing regions encompass the high enstrophy, strongly swirling 'worms'. These 'worms' induce high local strain fields leading to the formation of dissipation 'sheets', thereby revealing enstrophy production to be a complex interaction between rotation and strain the skew-symmetric and symmetric components of the velocity gradient tensor, respectively.