Relative dispersion in isotropic turbulence. Part 1. Direct numerical simulations and Reynolds-number dependence
Relative dispersion in isotropic turbulence. Part 1. Direct numerical simulations and Reynolds-number dependence
复制标题
各向同性湍流中的相对色散。
DOI：
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发表时间：
2004
影响因子：
3.7
通讯作者：
M. Borgas
中科院分区：
文献类型：
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作者：
P. Yeung;M. Borgas
采用直接数值模拟研究了各向同性湍流中流体颗粒对的相对弥散，比以前报道的更详细，覆盖更宽的雷诺数范围。一个主要的动机是提供一个重要的资源，随机建模，将信息的数量依赖。从小于一个Kolmogorov长度尺度大于一个整数长度尺度的粒子对初始分离，泰勒尺度雷诺数从约38至230的详细结果。注意几个来源的不确定性，包括样本量的要求，单粒子拉格朗日Kolmogorov常数的值，和统计稳定湍流的空间平均量的时间变化。相对色散分析的两粒子分离矢量的大小和角取向的演变。早期的统计数据是一致的欧拉空间结构的流量，而大的时间行为是一致的粒子对远离独立移动。然而，在中间时间的顺序几个柯尔莫哥洛夫时间尺度，特别是对于小的初始分离和较高的雷诺数，无论是分离距离和它的变化率（称为分离速度）是高度间歇性的，与平坦度因子远高于欧拉速度差的空间。这种强烈的不稳定性是相对分散的结果，其受到湍流中宽范围的长度尺度的影响，因为一些颗粒对漂移得相对较远。数值证据表明，大量的分散发生在垂直于初始分离矢量的平面中，这意味着该矢量的方向，特别是对于小的初始分离，只有有限的重要性。
The relative dispersion of fluid particle pairs in isotropic turbulence is studied using direct numerical simulation, in greater detail and covering a wider Reynolds number range than previously reported. A primary motivation is to provide an important resource for stochastic modelling incorporating information on Reynolds-number dependence. Detailed results are obtained for particle-pair initial separations from less than one Kolmogorov length scale to larger than one integral length scale, and for Taylor-scale Reynolds numbers from about 38 to 230. Attention is given to several sources of uncertainty, including sample size requirements, value of the one-particle Lagrangian Kolmogorov constant, and the temporal variability of space-averaged quantities in statistically stationary turbulence. Relative dispersion is analysed in terms of the evolution of the magnitude and angular orientation of the two-particle separation vector. Early-time statistics are consistent with the Eulerian spatial structure of the flow, whereas the large-time behaviour is consistent with particle pairs far apart moving independently. However, at intermediate times of order several Kolmogorov time scales, and especially for small initial separation and higher Reynolds numbers, both the separation distance and its rate of change (called the separation speed) are highly intermittent, with flatness factors much higher than those of Eulerian velocity differences in space. This strong intermittency is a consequence of relative dispersion being affected by a wide range of length scales in the turbulent flow as some particle pairs drift relatively far apart. Numerical evidence shows that substantial dispersion occurs in the plane orthogonal to the initial separation vector, which implies that the orientation of this vector has, especially for small initial separation, only limited importance.