The main objective of this work is to predict the mixing of two different miscible oils in a very long channel. The background to this problem relates to the mixing of heavy and light oil in a pipeline. As a first step, a 2D channel with an aspect ratio of 250 is considered. The batch-mixing of two miscible crude oils with different viscosities and densities is modeled using an unsteady laminar model and unsteady RANS model available in the commercial CFD solver ANSYS-Fluent. For a comparison, a LES model was used for a 3D version of the 2D channel. The distinguishing feature of this work is the Lagrangian coordinate system utilized to set no-slip wall boundary conditions. The global CFD model has been validated against classical analytical solutions. Excellent agreement has been achieved. Simulations were carried out for a Reynolds number of 6300 (calculated using light oil properties) and a Schmidt number of \(~10^4\). The results show that, in contrast to the unsteady RANS model, the LES and unsteady laminar models produce comparable mixing dynamics for two oils in the channel. Analysis of simulations also shows that, for a channel length of 100 m and a height of 0.4 m, the complete mixing of two oils across the channel has not been achieved. We showed that the mixing zone consists of the three different mixing sub-zones, which have been identified using the averaged mass fraction of the heavy oil along the flow direction. The first sub-zone corresponds to the main front propagation area with a length of several heights of the channel. The second and third sub-zones are characterized by so-called shear-flow-driven mixing due to the Kelvin–Helmholtz vortices occurring between oils in the axial direction. It was observed that the third sub-zone has a steeper mass fraction gradient of the heavy oil in the axial direction in comparison with the second sub-zone, which corresponds to the flow-averaged mass fraction of 0.5 for the heavy oil.

中文翻译：

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长通道原油批量混合的数值研究。

这项工作的主要目的是预测很长通道中两种不同混溶油的混合。该问题的背景涉及管道中重油和轻油的混合。第一步，考虑纵横比为250的2D通道。使用可在商业CFD求解器ANSYS-Fluent中使用的非稳态层流模型和非稳态RANS模型对两种粘度和密度不同的混溶原油进行分批混合建模。为了进行比较，将LES模型用于2D通道的3D版本。这项工作的显着特点是用于设置防滑墙边界条件的拉格朗日坐标系。全球CFD模型已针对经典分析解决方案进行了验证。达成了良好的协议。\（〜10 ^ 4 \）。结果表明，与非稳态RANS模型相反，LES和非稳态层流模型对通道中的两种油产生了可比的混合动力学。模拟分析还显示，对于100 m的通道长度和0.4 m的高度，尚未实现通道中两种油的完全混合。我们表明，混合区由三个不同的混合子区组成，已使用重油沿流动方向的平均质量分数确定了混合子区。第一子区域对应于具有数个通道高度的长度的主前传播区域。第二和第三子区域的特征是所谓的剪切流驱动混合，这是由于在油之间在轴向方向上发生了开尔文-亥姆霍兹旋涡。