Joint statistics of a passive scalar and its dissipation in turbulent flows
Joint statistics of a passive scalar and its dissipation in turbulent flows
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被动标量及其在湍流中的耗散的联合统计
DOI：
10.1017/s0022112094002892
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发表时间：
1994
影响因子：
3.7
通讯作者：
L. Fulachier
中科院分区：
文献类型：
--
作者：
F. Anselmet;H. Djeridi;L. Fulachier
被动标量及其耗散之间的统计关系对于基本理解湍流的小尺度性质和湍流燃烧模拟的各个方面都是重要的。利用谱分析和概率密度函数，以温度作为被动标量，在两种不同的流动中研究了这一问题。文中特别注意了与温度耗散有关的三个平方导数的实验测定。作为第一步，我们发现温度及其耗散之间的相关系数等基本性质与标量涨落的不对称性有很强的相关性，因此通常假设的这些变量之间的统计独立性是不成立的。这些趋势对于这里研究的两种流动是相同的，一种是边界层，一种是急流。这种联系似乎与两个量的小幅度波动有关，而这两个量的波动与介于积分尺度和泰勒微尺度之间的相对较低的频率有关。在温度偏度因子几乎为零的地区，相关系数也很小，几项测试表明，独立的假设是完全合理的。因此，影响温度及其耗散联合统计量的主要参数是温度起伏的非对称性，但纵向温度导数的不对称性也涉及到，纵向温度导数是由流动边界条件引起的，通常通过所谓的温度梯度的存在而感觉到。即使导数偏度因子的大小在两个流动中几乎均匀分布，但在温度不对称影响相对较弱的流动区域，次要效应成为主导效应。
The statistical relationship between a passive scalar and its dissipation is important for both a basic understanding of turbulence small-scale properties and for various aspects of turbulent combustion modelling. This problem is studied in two different flows through spectral analysis as well as probability density functions using temperature as a passive scalar. Particular attention is paid to the experimental determination of the three squared derivatives involved in the temperature dissipation. As a first step, it is found that basic properties such as the correlation coefficient between temperature and its dissipation are strongly related to the asymmetry of the scalar fluctuations, so that the usually assumed statistical independence between these variables is not justified. These trends are the same for the two flows investigated here, a boundary layer and a jet. This connection appears to be related to fluctuations of small amplitude for both quantities which are associated with relatively low frequencies lying between the integral scale and the Taylor microscale. In regions where the temperature skewness factor is nearly zero, the correlation coefficient is also very small, and several tests show that the assumption of independence is then fully justified. Thus, the main parameter influencing joint statistics of temperature and its dissipation is the asymmetric feature of temperature fluctuations, but the asymmetry of the longitudinal temperature derivative, which results from the flow boundary conditions and is usually felt through the presence of the so-called temperature ramps, is also involved. Even though the magnitude of the derivative skewness factor is almost uniformly distributed in both flows, the secondary effect becomes the dominant one in flow regions where the influence of the temperature asymmetry is relatively weak.