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arXiv 2005.12456physics.flu-dyn
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在有壁turbulence压缩表示中局部涡识别准则的有效性

On the effectiveness of local vortex identification criteria in the compressed representation of wall-bounded turbulence

Chengyue Wang, Qi Gao, Biao Wang

摘要:

将复杂的流动压缩成一团涡丝是涡表象的经典概念的基本含义。为了从已有的速度场中提取涡丝,人们提出了各种涡的识别准则,这是涡表示的一个基本步骤。本文的工作重点是这些识别标准的有效性在压缩表示的壁有界湍流。五个本地识别标准的涡强度和三个标准的涡轴被认为是。为了便于比较,这项工作首先无量纲化的涡强度的标准的基础上,其尺寸和均方根,与相应的等效阈值规定。通过试验涡强度和涡轴识别准则的所有可能组合,讨论了涡矢量的最佳定义。这些准则在压缩表示中的有效性基于两个原则进行评估:(1)有效压缩,这意味着所需的信息越少,表示越好;(2)精确解压缩,这强调原始速度场可以基于涡表示以高精度重建。在实际应用中,定量地比较了用这些准则识别涡轴和涡等值面的对齐情况,以及解压缩速度场的精度。利用微分几何的方法描述对准度,并通过基于二维场的线性随机估计实现解压缩过程。本文的研究结果为涡识别准则在有壁湍流中的应用提供了一定的参考。

英文摘要:

Compressing complex flows into a tangle of vortex filaments is the basic implication of the classical notion of the vortex representation. Various vortex identification criteria have been proposed to extract the vortex filaments from available velocity fields, which is an essential procedure in the practice of the vortex representation. This work focuses on the effectiveness of those identification criteria in the compressed representation of wall-bounded turbulence. Five local identification criteria regarding the vortex strength and three criteria for the vortex axis are considered. To facilitate the comparisons, this work first non-dimensionalize the criteria of the vortex strength based on their dimensions and root mean squares, with corresponding equivalent thresholds prescribed. The optimal definition for the vortex vector is discussed by trialling all the possible combinations of the identification criteria for the vortex strength and the vortex axis. The effectiveness of those criteria in the compressed representation is evaluated based on two principles: (1) efficient compression, which implies the less information required, the better for the representation; (2) accurate decompression, which stresses that the original velocity fields could be reconstructed based on the vortex representation in high accuracy. In practice, the alignment of the identified vortex axis and vortex isosurface, and the accuracy for decompressed velocity fields based on those criteria are quantitatively compared. The alignment degree is described by using the differential geometry method, and the decompressing process is implemented via the two-dimensional field-based linear stochastic estimation. The results of this work provide some reference for the applications of vortex identification criteria in wall-bounded turbulence.

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