Toward High-Order CFD-DEM: Development and Validation

Abstract

CFD-DEM is used to simulate solid−fluid systems. DEM models the motion of discrete particles while CFD models the dynamics of the fluid phase. Coupling both necessitates the calculation of the void fraction and the solid−fluid forces resulting in a computationally expensive method. Additionally, evaluating volume-averaged quantities locally restricts particle to cell size ratios limiting the accuracy of the CFD. To mitigate these limitations, we develop a unified finite element CFD-DEM solver which integrates the CFD and DEM solvers into a single software resulting in faster and cheaper coupling between the solvers. It supports dynamically load-balanced parallelization. This allows for more efficient simulations as load balancing ensures the even distribution of workloads among processors; thus, exploiting available resources efficiently. Our solver supports high order schemes; thus, allowing the use of larger elements enhancing the validity and stability of the void fraction schemes while achieving better accuracy. We verify and validate our CFD-DEM solver with a large array of test cases: particle sedimentation, a fluidized bed, the Rayleigh Taylor instability, and a spouted bed.

Quadrature-Centered Averaging Scheme for Accurate and Continuous Void Fraction Calculation in Computational Fluid Dynamics–Discrete Element Method Simulations

“…We aim at validating our void fraction scheme by studying its effect on fluidization. For this purpose, we simulate using the CFD-DEM solver in Lethe the same flat bubbling spouted bed as Wu et al and we compare with their simulation results as well as the experimental results and the simulation results by Bokkers et al It is important to note that Wu et al and Bokkers et al used the hard sphere model in their simulations for the DEM. However, our solver uses the soft sphere model.…”

“…In order to demonstrate the spatial and temporal continuity of the quadrature-centered method void fraction scheme, we simulate a test case of particle sedimentation in water using the CFD-DEM solver in Lethe. 30 We compare this method with two different void fraction schemes: the particle-centered method and the satellite point method. Only these methods are evaluated as they represent well-known methods frequently used and which are relatively simple to implement in a software parallelized using distributed memory parallelization (MPI).…”

“…For more details on the description of the particle−fluid forces, we refer the reader to the Lethe CFD-DEM article. 30 We also choose R s as to obtain a volume-averaging sphere with the same volume as the element (Ω) in which its center is located, so that R s…”

“…In order to demonstrate the spatial and temporal continuity of the quadrature-centered method void fraction scheme, we simulate a test case of particle sedimentation in water using the CFD-DEM solver in Lethe . We compare this method with two different void fraction schemes: the particle-centered method and the satellite point method.…”

“…In an attempt to overcome the limitations concerning computational efficiency, accuracy, and stability which many methods suffer from, we aim at decoupling the averaging volume from the computational cell size. We therefore develop a new analytical void fraction scheme in the context of the finite element method and implement it in the open source CFD-DEM software Lethe. − The scheme calculates the void fraction in a volume-averaging sphere centered at the quadrature point which is where we are interested in determining the void fraction. Our developed scheme is analytical since it involves the calculation of intersections between particles and volume-averaging spheres, and it is cheaper than current analytical methods since sphere–sphere intersections are much simpler to evaluate than sphere–polyhedron intersections.…”