On artificial density treatment for the pressure Poisson equation in the DEM-CFD simulations
On artificial density treatment for the pressure Poisson equation in the DEM-CFD simulations
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DOI：
10.1016/j.powtec.2020.05.116
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发表时间：
2020-07
影响因子：
5.2
通讯作者：
Y. Mori;K. Takabatake;Yoshiharu Tsugeno;M. Sakai
中科院分区：
文献类型：
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作者：
Y. Mori;K. Takabatake;Yoshiharu Tsugeno;M. Sakai
离散单元法(DEM)与计算流体力学(CFD)相结合被认为是气固两相流动数值计算的标准方法。当DEM-CFD方法应用于工业系统的模拟时，我们不能回避对任意形状的墙体边界的建模。最近，我们在DEM-CFD模拟中开发了一种创新的壁面边界模型，其中DEM和CFD中的壁面边界使用了符号距离函数(SDF)和浸没边界方法(IBM)。SDF使基于标量场创建任意形状的墙边界成为可能。通过在CFD网格中反映局部体积分数上的SDF点数，可以将IBM用于壁面边界模型。因此，将SDF与IBM相结合，可以方便地在DEM-CFD方法中生成任意形状的墙体边界。另一方面，作者小组指出了密度尺度技术在CFD中应用的必要性。在密度标度技术中，在压力泊松方程的计算中考虑了密度标度系数。将SDF/IBM应用于CFD而不采用密度标度技术时，可能会出现非自然流体通过壁面边界物体的情况。到目前为止，密度标度系数对气固两相流的影响还没有被研究过。在此背景下，本文研究了密度尺度系数对气固两相流动的影响。通过这项研究，指出了在DEM-CFD模拟中使用IBM作为墙体边界时，引入密度比例技术是至关重要的。结果表明，密度标度系数不是由理论决定的，而是由经验决定的，在典型的气固两相流动系统中，密度标度系数应在100~1000之间。此外，还说明了DEM-CFD模拟中密度尺度系数的取值不影响计算成本。
The discrete element method (DEM) coupled with computational fluid dynamics (CFD) is regarded to be a standard approach in a numerical calculation of gas-solid flow. When the DEM-CFD method is applied to the simulation of industrial systems, we cannot shy away from the modeling of arbitrary shape wall boundaries. Very recently, we have developed an innovative wall boundary model in the DEM-CFD simulations, where the signed distance function (SDF) and the immersed boundary method (IBM) are used for the wall boundary in the DEM and CFD. The SDF makes it possible to create an arbitrary shape wall boundary based on the scalar field. The IBM can be used for the wall boundary model by reflecting the number of the SDF points on the local volume fraction in CFD grid. Thus, the arbitrary shape wall boundary can be easily created in the DEM-CFD method by combining the SDF with the IBM. On the other hand, the authors' group has pointed out the necessity of the density scale technique in CFD. In the density scale technique, the density scale coefficient is considered in the calculation of the pressure Poisson equation. When the SDF/IBM is applied to CFD without density scaling technique, an unnatural fluid flow might occur through the wall boundary object. The effect of the density scaling coefficient on a gas-solid flow has not been examined so far. From this background, the influence of the density scale coefficient on a gas-solid flow is investigated in the present study. Through this study, introduction of the density scaling technique is designated to be crucial when the IBM is used for the wall boundary in the DEM-CFD simulation. The density scaling coefficient is shown to be decided not by theory but by experience, and the value should become 100 to 1000 in a typical gas-solid flow system. Besides, it is illustrated that the calculation cost is not influenced by the value of the density scale coefficient in the DEM-CFD simulations.