Scalar gradients in stirred mixtures and the deconstruction of random fields
Scalar gradients in stirred mixtures and the deconstruction of random fields
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DOI：
10.1017/jfm.2016.799
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发表时间：
2017-01
影响因子：
3.7
通讯作者：
T. Le Borgne;P. Huck;M. Dentz;E. Villermaux
中科院分区：
文献类型：
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作者：
T. Le Borgne;P. Huck;M. Dentz;E. Villermaux
提出了一种预测非均质流中标量梯度（或浓度差）分布的一般理论。通过对在流体拉伸作用下自然形成的基本层状结构的演化分析，量化了标量场的演化。标量场中的空间相关性和浓度梯度因此通过拉伸薄片的扩散聚集而发展。邻近空间位置的浓度水平是由片层聚集的历史造成的，这在一定程度上是两个位置共同的。浓度差异消除了这一共同部分，因此只依赖于独立聚集的片层。利用这一原理，我们提出了一种理论，该理论设想浓度增量是基本片层组合解构的结果。该框架提供了一系列流动系统（包括湍流和低雷诺数多孔介质流动）在任何空间增量上的浓度增量概率密度函数（pdf）的解析表达式，用于受限和分散混合物。通过这种解构原理，标量增量分布揭示了构建标量场的基本拉伸和聚集机制。
A general theory for predicting the distribution of scalar gradients (or concentration differences) in heterogeneous flows is proposed. The evolution of scalar fields is quantified from the analysis of the evolution of elementary lamellar structures, which naturally form under the stretching action of the flows. Spatial correlations in scalar fields, and concentration gradients, hence develop through diffusive aggregation of stretched lamellae. Concentration levels at neighbouring spatial locations result from a history of lamella aggregation, which is partly common to the two locations. Concentration differences eliminate this common part, and thus depend only on lamellae that have aggregated independently. Using this principle, we propose a theory which envisions concentration increments as the result of a deconstruction of the basic lamella assemblage. This framework provides analytical expressions for concentration increment probability density functions (PDFs) over any spatial increments for a range of flow systems, including turbulent flows and low-Reynolds-number porous media flows, for confined and dispersing mixtures. Through this deconstruction principle, scalar increment distributions reveal the elementary stretching and aggregation mechanisms building scalar fields.