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

计算流体力学（CFD）与粗粒离散元法（CFD- 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），将选定数量的粒子组合成一个有代表性的包。这大大减少了需要跟踪的粒子数量，并导致了巨大的加速。因此，它是一种很有前途的模拟工业规模颗粒系统的方法。与经典DEM一样，通过求解牛顿运动定律计算每个包裹的轨迹，并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理论，粒子-粒子、粒子-壁和粒子-流体相互作用的力需要被标度。在过去的几年中，许多作者提出了几种缩放方法，但尚未对这些方法进行系统的比较。所要求的项目将从不同的扩展方法的基本和系统的比较开始。目的是找到在广泛的比例因子范围内给出可靠结果的比例方法。初步研究表明，特征反应器长度与包径之比不应超过一定限度。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。研究人员将研究这种方法是否能使CFD-CGDEM有效地用于内部紧密堆积的反应堆，这在可能的技术应用中尤其重要。原始的CFD-DEM要求是细胞比颗粒大。因此，粗粒化会导致网格的固有粗化。这就是为什么重要的中尺度效应（如团簇形成）无法解决的原因。如果不考虑细胞大小要求的方法能提高CFD-CGDEM的准确性，我们将对此进行研究。此外，还将检验使用过滤阻力模型模拟中尺度效应是否对结果质量有积极影响。目前，关于CFD-CGDEM在多分散颗粒系统中的可用性的研究很少，而且非常基础。正确预测粒子偏析的重要方面尚未得到研究。该项目的目的是弥补这一差距，并评估是否可以在原则上使用CFD-CGDEM来预测双分散颗粒系统的分离行为。基于已开发的方法，CFD-CGDEM将用于模拟包括内部在内的工业相关案例。单分散和双分散系统将被研究。目的是证明CFD-CGDEM是一种高效可靠的方法，用于模拟“真实世界”的颗粒系统，并确定其应用限制。

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.