Geometrical and Taylor dispersion in a fracture with random obstacles: An experimental study with fluids of different rheologies
Geometrical and Taylor dispersion in a fracture with random obstacles: An experimental study with fluids of different rheologies
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DOI：
10.1029/2007wr006403
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发表时间：
2008-06
影响因子：
5.4
通讯作者：
A. Boschan;I. Ippolito;R. Chertcoff;H. Auradou;L. Talon;J. Hulin
中科院分区：
文献类型：
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作者：
A. Boschan;I. Ippolito;R. Chertcoff;H. Auradou;L. Talon;J. Hulin
用光学方法研究了一种具有相同流变性能的牛顿流体或剪切稀化流体与另一种具有相同流变性能的流体的混相位移。在局部尺度上，单个像素上的浓度变化与局部传输时间（x, y）和色散率ld（x, y）满足高斯对流色散关系。ld随pims数Pe的变化表明，它是几何色散和泰勒色散共同作用的结果，分别在低Pe值和高Pe值处占主导地位。使用剪切稀释溶液代替牛顿流体可以增强速度对比（从而增强几何色散）并降低泰勒色散。在全球尺度上，从等浓度线c = 0.5（相当于常数（x, y）值线）开始研究锋面几何形状：在过渡旅行时间之后，它们在平行于流动方向上的宽度达到一个常数极限，与Log（Pe）线性变化，斜率随着流体的剪切减薄特性而增加。这些特征与先前对其他具有自仿射粗糙度的模型裂缝的观察结果进行了比较，这些裂缝具有通道化效应。
The miscible displacement of a Newtonian or shear‐thinning fluid by another one of same rheological properties has been studied optically in a flat transparent model fracture with a random distribution of identical cylindrical obstacles on one of the walls. At the local scale, the concentration variation on individual pixels satisfies a Gaussian convection‐dispersion relation with local transit time (x, y) and dispersivity ld(x, y). The variation of ld with the Péclet number Pe shows that it results from a combination of geometrical and Taylor dispersion, respectively dominant at low and high Pe values. Using shear‐thinning solutions instead of a Newtonian fluid enhances the velocity contrasts (and therefore geometrical dispersion) and reduces Taylor dispersion. At the global scale, the front geometry is studied from the isoconcentration lines c = 0.5 (equivalent to lines of constant (x, y) value): beyond a transition travel time, their width in the direction parallel to the flow reaches a constant limit varying linearly with Log(Pe) with a slope increasing with the shear‐thinning character of the fluid. These characteristics are compared to previous observations on other model fractures with a self‐affine roughness displaying channelization effects.