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On the thresholds of vortex visualisation methods
International Journal of Computational Fluid Dynamics ( IF 1.3 ) Pub Date : 2020-04-15 , DOI: 10.1080/10618562.2020.1745781
Yinlin Dong 1 , Wufeng Tian 2
Affiliation  

Since the discovery of vortex structures in turbulence, research in the area of vortex visualisation methods has been of interest. The prevalent Galilean invariant visualisation methods, like Q, Lambda2, and Omega methods, are based on the local pointwise analysis of invariants of the velocity gradient tensor. When plotting the vortex iso-surfaces, different methods will introduce different thresholds for visualisation purpose. Varying the thresholds can greatly change the appearance of the results and the interpretation can be significantly different for the same flow phenomenon. Using our direct numerical simulation data on late stage laminar turbulent boundary layer transition, we will investigate the similarities and differences among several prevailing vortex visualisation methods caused by the selection of thresholds. The sensitivity of thresholds are further explored analytically in a few flow examples. In addition, we propose an appropriate usage of the threshold which will result in remarkably similar looking vortex structures.

中文翻译:

关于涡流可视化方法的阈值

自从发现湍流中的涡旋结构以来,涡旋可视化方法领域的研究就引起了人们的兴趣。流行的伽利略不变量可视化方法,如 Q、Lambda2 和 Omega 方法,都是基于速度梯度张量不变量的局部逐点分析。在绘制涡流等值面时,不同的方法将引入不同的阈值以用于可视化目的。改变阈值可以极大地改变结果的外观,并且对相同的流动现象的解释可能会有很大的不同。使用我们对后期层流湍流边界层过渡的直接数值模拟数据,我们将研究由阈值选择引起的几种流行的涡旋可视化方法之间的异同。在一些流示例中进一步分析了阈值的敏感性。此外,我们建议适当使用阈值,这将导致看起来非常相似的涡旋结构。
更新日期:2020-04-15
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