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首页> 外文期刊>Physics of fluids >Coherent vortices in high resolution direct numerical simulation of homogeneous isotropic turbulence: A wavelet viewpoint
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Coherent vortices in high resolution direct numerical simulation of homogeneous isotropic turbulence: A wavelet viewpoint

机译：均质各向同性湍流高分辨率直接数值模拟中的相干涡：小波视角

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Coherent vortices are extracted from data obtained by direct numerical simulation (DNS) of three-dimensional homogeneous isotropic turbulence performed for different Taylor microscale Reynolds numbers, ranging from Re-lambda=167 to 732, in order to study their role with respect to the flow intermittency. The wavelet-based extraction method assumes that coherent vortices are what remains after denoising, without requiring any template of their shape. Hypotheses are only made on the noise that, as the simplest guess, is considered to be additive, Gaussian, and white. The vorticity vector field is projected onto an orthogonal wavelet basis, and the coefficients whose moduli are larger than a given threshold are reconstructed in physical space, the threshold value depending on the enstrophy and the resolution of the field, which are both known a priori. The DNS dataset, computed with a dealiased pseudospectral method at resolutions N=256(3), 512(3), 1024(3), and 2048(3), is analyzed. It shows that, as the Reynolds number increases, the percentage of wavelet coefficients representing the coherent vortices decreases; i.e., flow intermittency increases. Although the number of degrees of freedom necessary to track the coherent vortices remains small (e.g., 2.6% of N=2048(3) for Re-lambda=732), it preserves the nonlinear dynamics of the flow. It is thus conjectured that using the wavelet representation the number of degrees of freedom to compute fully developed turbulent flows could be reduced in comparison to the standard estimation based on Kolmogorov's theory. (c) 2007 American Institute of Physics.
机译：从通过对Re-lambda = 167到732范围内的不同Taylor微尺度雷诺数执行的三维均质各向同性湍流进行直接数值模拟（DNS）获得的数据中提取相干涡，以研究其对流的作用间断性。基于小波的提取方法假定相干涡旋在去噪后仍然存在，而无需任何形状的模板。最简单的猜测是对被认为是加性，高斯和白色的噪声进行假设。将涡度矢量场投影到正交小波基础上，并在物理空间中重构其模量大于给定阈值的系数，该阈值取决于场的涡旋和分辨率，这都是先验的。分析了使用脱磷伪光谱方法以分辨率N = 256（3），512（3），1024（3）和2048（3）计算的DNS数据集。它表明，随着雷诺数的增加，代表相干涡的小波系数的百分比降低;即，流量间歇性增加。尽管跟踪相干涡旋所需的自由度数量仍然很小（例如，对于Re-lambda = 732，为N = 2048（3）的2.6％），但它保留了流动的非线性动力学。因此可以推测，与基于Kolmogorov理论的标准估计相比，使用小波表示法可以减少计算完全展开的湍流的自由度。 （c）2007年美国物理研究所。

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