Development and verification of an unresolved CFD-DEM method applicable to different-sized grids

Abstract

The traditional unresolved CFD-DEM method is designed for fluid grid sizes larger than particle sizes, and improved methods are imperative when encountering cases with fluid grid sizes comparable to particle sizes. This study attempts to develop an unresolved CFD-DEM method that applies to different-sized grids and can be easily implemented on commercial platforms using unstructured grids, aiming to greatly help engineers solve engineering problems without investing much effort into choosing appropriate simulation methods and designing fluid grids. To this end, the new method considers interphase force correction at the particle level and field smoothing at the cell level by constructing a spherical search area whose size is determined by particle sizes. Mass conservation is strictly guaranteed in the new method, which is essential to simulations involving chemical reactions. The accuracy and universality of the new method are comprehensively evaluated by two test cases. The first test case is conducted in a spouted bed discretized by unstructured grids of three sizes. The results demonstrate that the new method not only applies to comparable-sized grids but can yield the same predictions as the traditional method in large-sized grids. In other words, the new method is universal as long as grid sizes lie at the unresolved level. Thanks to the simplicity of the algorithm, the new method does not compromise calculation efficiency. The second test case is conducted in a draft tube-type feeder discretized by non-uniform unstructured grids. By comparing with experimental measurements, the main features of flow patterns, pressure drop characteristics, and mass flow rates are reasonably predicted, confirming the capability of the new method to simulate complex gas-solid flows with non-uniform unstructured grids. Users do not need to make any adjustments to the new method once it is implemented on commercial platforms. In the future, the new method can potentially become a universal method to simulate gas-solid flows and greatly help engineers solve engineering problems.