An Adaptive Timestepping Algorithm for Particle Time Integration in Coupled CFD-DEM Simulations

Coupled Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) models provide an accurate description of multiphase physical systems where a granular phase exists in an underlying continuous medium. The time integration of the granular phase in these simulations are typically handled using an explicit time integration scheme with a global time step that is much smaller than fluid time scales, in order to resolve inter-particle collisions. An adpative time integration technique that avoids this global constraint for the granular phase is presented in this work. The algorithm involves the use of local time stepping to resolve collisional time scales for only a subset of particles that are in close proximity to potential collision partners, thereby resulting in significant reduction of computational cost. This approach is observed to be 2-3X faster than traditional explicit methods for problems that involve both dense and dilute regions, while maintaining the same level of accuracy.