On the geometry of turbulent mixing
On the geometry of turbulent mixing
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湍流混合的几何学
DOI：
10.1017/s0022112099005674
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发表时间：
1998
影响因子：
3.7
通讯作者：
C. Innocenti
中科院分区：
文献类型：
--
作者：
E. Villermaux;C. Innocenti
我们调查的时间演化的几何分布的被动标量连续注入到远场的湍流水射流的尺度d小于当地的湍流积分尺度。用激光诱导荧光技术对含射流轴线的平面切割的浓度场进行了定量研究。全球功能，如从源的标量色散，以及标量场的精细结构，进行了分析。特别是，我们定义的体积所占据的区域，其浓度大于一个给定的浓度阈值（支持的标量场）和该体积被封闭的表面（边界的支持）。测量体积和表面范围以及它们各自的分形维数作为时间t的函数，并且浓度阈值由不同注入尺寸d的初始浓度Cs/C 0归一化。所有这些量都显示出对t、d和Cs的明显依赖性，并且它们的演化随着变量τ =（ut/d）（Cs/C 0）而重新缩放，此外，分形维数是尺度依赖性的。在大尺度下，体积和表面的比表面积和分形维数趋于1，反映了小尺度下标量的片状结构。这些发现表明了湍流混合动力学的原始图像。
We investigate the temporal evolution of the geometrical distribution of a passive scalar injected continuously into the far field of a turbulent water jet at a scale d smaller than the local integral scale of the turbulence. The concentration field is studied quantitatively by a laser-induced- fluorescence technique on a plane cut containing the jet axis. Global features such as the scalar dispersion from the source, as well as the fine structure of the scalar field, are analysed. In particular, we define the volume occupied by the regions whose concentration is larger than a given concentration threshold (support of the scalar field) and the surface in which this volume is enclosed (boundary of the support). The volume and surface extents, and their respective fractal dimensions are measured as a function of time t, and the concentration threshold is normalized by the initial concentration Cs/C0 for different injection sizes d. All of these quantities display a clear dependence on t, d and Cs, and their evolutions rescale with the variable ξ = (ut/d)(Cs/C0), the fractal dimension being, in addition, scale dependent. The surface-to-volume ratio and the fractal dimension of both the volume and the surface tend towards unity at large ξ, reflecting the sheet-like structure of the scalar at small scales. These findings suggest an original picture of the kinetics of turbulent mixing.