The effects of resolution and noise on kinematic features of fine-scale turbulence
The effects of resolution and noise on kinematic features of fine-scale turbulence
复制标题
分辨率和噪声对细尺度湍流运动学特征的影响
DOI：
10.1007/s00348-011-1159-2
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发表时间：
2011
影响因子：
2.4
通讯作者：
Buxton O
中科院分区：
文献类型：
--
作者：
Buxton O
通过比较数值数据和实验数据，研究了空间分辨率和实验噪声对剪切流湍流运动学精细尺度特征的影响。名义上二维平面混合层的直接数值模拟（DNS）以四种不同的、逐渐变粗的空间分辨率均值过滤到均匀笛卡尔网格上。然后使用实验研究中常用的简单二阶方案计算空间梯度，以便在数值和先前获得的实验数据之间进行直接比较。正如预期的那样，与其他研究一致，我们发现空间分辨率的降低大大降低了高幅度速度梯度的频率，从而减少了应变（耗散）和旋转（熵）的标量类似物的间歇性。随着分辨率的粗化，物理空间中耗散和熵在空间上相干的距离也会增加，尽管这些距离保持恒定数量的网格点，这表明数据遵循所应用的滤波器。随着空间分辨率的降低，在应变率张量的特征值中也观察到这种间歇性的减少。这些特征值归一化的量被证明是极其重要的，因为精细尺度量（例如柯尔莫哥洛夫长度尺度）会随着不同的空间分辨率而变化。当用局部柯尔莫哥洛夫尺度标准化时，这会导致这些特征值的模态值发生轻微变化，而当用大尺度、与分辨率无关的量标准化时，不会观察到这种变化。应变和旋转之间的相互作用通过速度梯度张量特征方程 Q 和 R 的第二个和第三个不变量之间的联合概率密度函数 (pdf) 以及应变率张量和涡度矢量的特征向量之间的对齐来检查。高斯噪声会增加数据集的发散误差，从而影响 Q–Rjointpdf 和对齐余弦的大小。实验数据集的行为在质量上与添加高斯噪声的数值数据集相似，证实了理解粗略解析的噪声实验数据的局限性的重要性。
The effect of spatial resolution and experimental noise on the kinematic fine-scale features in shear flow turbulence is investigated by means of comparing numerical and experimental data. A direct numerical simulation (DNS) of a nominally two-dimensional planar mixing layer is mean filtered onto a uniform Cartesian grid at four different, progressively coarser, spatial resolutions. Spatial gradients are then calculated using a simple second-order scheme that is commonly used in experimental studies in order to make direct comparisons between the numerical and previously obtained experimental data. As expected, consistent with other studies, it is found that reduction of spatial resolution greatly reduces the frequency of high magnitude velocity gradients and thereby reduces the intermittency of the scalar analogues to strain (dissipation) and rotation (enstrophy). There is also an increase in the distances over which dissipation and enstrophy are spatially coherent in physical space as the resolution is coarsened, although these distances remain a constant number of grid points, suggesting that the data follow the applied filter. This reduction of intermittency is also observed in the eigenvalues of the strain-rate tensor as spatial resolution is reduced. The quantity with which these eigenvalues is normalised is shown to be extremely important as fine-scale quantities, such as the Kolmogorov length scale, are showed to change with different spatial resolution. This leads to a slight change in the modal values for these eigenvalues when normalised by the local Kolmogorov scale, which is not observed when they are normalised by large-scale, resolution-independent quantities. The interaction between strain and rotation is examined by means of the joint probability density function (pdf) between the second and third invariants of the characteristic equation of the velocity gradient tensor,QandRrespectively and by the alignments between the eigenvectors of the strain-rate tensor and the vorticity vector. Gaussian noise is shown to increase the divergence error of a dataset and subsequently affect both theQ–Rjointpdfand the magnitude of the alignment cosines. The experimental datasets are showed to behave qualitatively similarly to the numerical datasets to which Gaussian noise has been added, confirming the importance of understanding the limitations of coarsely resolved, noisy experimental data.
影响因子：
3.7
作者：
Buxton, O. R. H.;Ganapathisubramani, B.
通讯作者：
Ganapathisubramani, B.
相干耗散尺度结构的层析 PIV 测量
影响因子：
3.2
作者：
N. Worth
通讯作者：
N. Worth
DOI：
--
发表时间：
1994
期刊：
影响因子：
--
作者：
R. Antonia;Yonggang Zhu;John Kim
通讯作者：
John Kim