Abstract

The Eulerian–Lagrangian approach is commonly employed in particulate flows, which can be classified into two subcategories: unresolved computational fluid dynamics-discrete element method (CFD–DEM) and resolved CFD–DEM. When the particle sizes are comparable to the cell sizes, the interphase coupling is not straightforward anymore and both the conventional unresolved CFD–DEM and resolved CFD–DEM are not applicable. In this paper, we propose a simple and novel coupling method for projecting and reconstructing the particle and interphase quantities, which is also called semi-resolved CFD–DEM. The particle quantities are uniformly distributed to the surrounding cells by expanding the fluid domain. The fluid phase quantities at the particle location are also reconstructed from the surrounding cells. Then, the relative velocity and the local void fraction for calculating the drag force are corrected. The expanding factor for the fluid domain is determined by comparing the drag force of the semi-resolved CFD–DEM with the resolved CFD–DEM results. It is found that the expanding factor increases linearly with the autocorrelation length. The developed method is validated by the simulation of a particle sedimentation and a sediment transport process, which proves that the present semi-resolved CFD–DEM fills the gap between the resolved and unresolved CFD–DEM. The difference between the implicit and explicit treatment of momentum exchange term is also discussed, and the explicit treatment shows better performance for large particles.

中文翻译：

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一种简单新颖的基于统一核近似的 CFD-DEM 建模耦合方法

摘要

欧拉-拉格朗日方法常用于颗粒流，可分为两个子类：未解析的计算流体动力学-离散元法（CFD-DEM）和解析的CFD-DEM。当颗粒尺寸与泡孔尺寸相当时，相间耦合不再简单，传统的未解析 CFD-DEM 和解析 CFD-DEM 均不再适用。在本文中，我们提出了一种简单而新颖的耦合方法来投影和重建粒子和相间量，也称为半解析CFD-DEM。通过扩大流体域，粒子数量均匀分布到周围的细胞。粒子位置处的流体相量也可以从周围的单元重建。然后，校正用于计算曳力的相对速度和局部空隙率。流体域的扩展因子是通过将半解析 CFD-DEM 的拖曳力与解析 CFD-DEM 结果进行比较来确定的。发现扩展因子随着自相关长度线性增加。所开发的方法通过颗粒沉降和沉积物传输过程的模拟进行了验证，证明目前的半解析 CFD-DEM 填补了解析和未解析 CFD-DEM 之间的空白。还讨论了动量交换项的隐式处理和显式处理之间的差异，并且显式处理对于大颗粒表现出更好的性能。