This paper was produced for the 2019 NAFEMS World Congress in Quebec Canada
The Discrete Element Method (DEM) is a powerful method for the simulation of flows of particles and powders. It is used to simulate collections of single particles as well as parcels of particles. Typically, the DEM can be used as a standalone method in case of larger grains where the influence of the interstitial fluid (e.g., gas) can be neglected.
When coupled to CFD using the volume-averaged Navier-Stokes equations, CFD-DEM models can cover a wide range of multi-phase flows, including flow of fine powders and their interaction with the interstitial gas phase, slurries and particles immersed in liquid, as well as flows involving droplets and bubbles. We first briefly outline the governing equations, and possible extensions of the modelling approach to model multi-phase flow, powder compaction, dust flow and electromagnetics.
We also give an overview regarding material parameter calibration for DEM and CFD-DEM simulations. For granular materials and powders the properties vary greatly due to their complex nature and depend on the source of the material, fluctuations in product quality, storage conditions and many more influence factors. Subsequently, it is usually not possible to take the material parameters from a textbook, but rather characterization experiments are performed and calibration methods using quality functions and optimization routines are used to find the set of material parameters that offer the best fit for the problem.
To underline the impact and effectiveness of the methods and the approach, we present two industrial use cases:
1. A DEM simulation of a bucket excavation process
2. A CFD-DEM simulation of a three-phase fluidized bed
For the first use case, we report on scale testing of a dragline bucket, including comparison to physical testing, and full-scale simulation of an actual bucket model.
The second use case, a 3-phase fluidized bed containing liquid, gas and solid, is discussed. An Euler-Euler multiphase framework coupled to DEM is used to scan a parameter range of operating conditions, which can then be used for process control or operator training.