Systematic Evaluation and Development of Discrete Element Coarse- Graining Approaches for the Modeling of Fluidized Particle Systems

计算流体动力学（CFD）与粗粒离散元法（CGDEM）的耦合是一种较新的、有效的颗粒系统数值模拟方法。基于离散元法（DEM）的颗粒的选择数量组合成一个代表性的地块。这大大减少了需要跟踪的粒子数量，并导致了巨大的速度提升。因此，这是一个很有前途的方法，在工业规模上的颗粒系统的模拟。像在经典的DEM中一样，每个包裹的轨迹通过求解牛顿运动定律来计算，并且使用适当的模型来描述接触和流体-颗粒相互作用。由于能量守恒或基于相似性理论，颗粒-颗粒、颗粒-壁和颗粒-流体相互作用力需要按比例缩放。在过去的几年里，许多作者提出了几种缩放方法，但这些方法的系统比较尚未完成。所要求的项目将首先对不同的缩放方法进行基本和系统的比较。目的是找到的缩放方法，给出了可靠的结果在广泛的缩放因子。初步研究表明，特征反应器长度与包裹直径的比率不应超过某一限度。将开发一种自适应粗粒化方法，以允许反应器内窄区域和宽区域的不同比例因子。将研究这种方法是否允许CFD-CGDEM有效地用于具有紧密填充的内部构件的反应器，这些内部构件在可能的技术应用中特别相关。最初的CFD-DEM要求是细胞大于颗粒。因此，粗粒化导致网格的固有粗化。这就是为什么重要的中尺度效应（例如，集群形成）不能被解决。将研究是否覆盖此单元尺寸要求的方法导致CFD-CGDEM的更高精度。此外，还将审查使用过滤阻力模型的中尺度效应模型是否对结果的质量有积极影响。到目前为止，只有很少的和非常基础的研究已经做了CFD-CGDEM的多分散颗粒系统的可用性。正确预测颗粒偏析的重要方面尚未得到研究。该项目的目的是缩小这一差距，并评估CFD-CGDEM原则上是否可用于预测双分散颗粒系统的分离行为。基于开发的方法CFD-CGDEM将用于模拟工业相关的情况下，包括内部。将研究单分散和双分散体系。目的是证明CFD-CGDEM是一种有效和可靠的方法，用于“真实的世界”的应用程序，以及识别应用限制的颗粒系统的模拟。

The coupling of Computational Fluid Dynamics (CFD) and a Coarse- Grained Discrete Element Method (CFD-CGDEM) is a relatively new and efficient numerical method for the simulation of particulate systems. Based on the Discrete Element Method (DEM) a chosen number of particles is combined into one representative parcel. This reduces the number of particles that need to be tracked significantly and leads to an enormous speed-up. Therefore, it is a promising method for the simulation of particulate systems on an industrial scale. Like in classical DEM the trajectories of each parcel are calculated by solving Newton’s law of motion and appropriate models are used to describe contact and fluid-particle interactions. Due to the conservation of energy or based on similarity theory the particle- particle, particle-wall, and particle-fluid interaction forces need to be scaled. In the last years, several scaling approaches by numerous authors were proposed, but a systematic comparison of those approaches has yet not been done. The requested project will start with a fundamental and systematic comparison of different scaling approaches. Aim is to find the scaling approach that gives reliable results over a wide range of scaling factors. Preliminary studies have shown that the ratio of characteristic reactor length to parcel diameter should not exceed a certain limit. An adaptive Coarse-Graining- Method will be developed to allow different scaling factors for narrow and wide regions within the reactor. It will be investigated if this approach allows CFD-CGDEM to be efficiently used for reactors with closely packed internals which are especially relevant in possible technical applications. An original CFD-DEM requirement is that the cells are bigger than the particles. Therefore, Coarse-Graining leads to an inherent coarsening of the mesh. That is why important meso-scale effects (e.g., cluster formation) cannot be resolved. It will be investigated if methods that override this cell size requirement lead to a higher accuracy of CFD-CGDEM. Furthermore, it will be examined if a modelling of meso-scale effects using filtered drag models has a positive effect on the quality of the results. By now only few and very basic studies have been done on the usability of CFD-CGDEM for poly-disperse particulate systems. The important aspect of a correct prediction of particle segregation has not yet been investigated. Aim of the project is to close this gap and to evaluate if CFD-CGDEM can in principle be used to predict the segregation behavior of bi- dispersed particulate systems. Based on the developed methods CFD-CGDEM will be used for the simulation of an industrially relevant case including internals. Mono- and bi-dispersed systems will be investi-gated. Aim is to prove that CFD-CGDEM is an efficient and reliable method for the simulation of particulate systems for “real world”-applications as well as to identify application limits.