(573d) Simulation of Stiffly Coupled Fluid-Particle Systems Involving Non-Spherical Particles: Robustness, Scalability, and Applications

Euler-Lagrange (EL) simulations involving particles with a typical size in the range of 1 to 100 micrometers are an important tool to understand disperse multiphase flows in nature and in industrial applications. Unfortunately, these simulations require a large number of time steps in case the relaxation time of suspended particles is small compared to relevant flow time scales.

In this talk we will present a number of coupling schemes that have been recently implemented into the open-source CFDEM® software package for spherical and non-spherical particles. These coupling schemes allow us to choose comparably large time steps, enabling the simulation of large-scale industrial systems within an acceptable amount of simulation time. Furthermore, a novel “Many-to-Many” communication scheme for heterogeneous domain decomposition will be presented. This scheme allows a more efficient exchange of Eulerian and Lagrangian data among CPUs, resulting in extremely efficient parallelization of EL simulations involving up to 128 CPUs.

We will illustrate our advances based on a number of benchmark problems. First, we will present results of verification simulations involving spherocylinders suspended in a liquid (e.g., motion in a Jeffery orbit, rebound from a wall). Second, results of one- and two-way coupled CFDEM simulations will be presented. Specifically, the motion of a dilute fibre suspension in a curved pipe was studied. For this flow configuration, secondary motion results in complex mixing and segregation effects of the fibre suspension. A newly implemented splitting technique of the coupling forces and torques, following the ideas of Fan and Ahmadi (J. Aerosol Sci. 26, 1995), allows significantly larger coupling intervals, leading to a substantial reduction in the computational cost of fibre-fluid simulations. Third, results of benchmark simulations using a newly implemented fibre-fibre interaction model in LIGGGHTS® will be presented. Specifically, the behavior of a large polydisperse fibre flock were studied, and statistics of the fibre orientation in the flock during compaction will be presented.

Acknowledgement
JDRP, LMK, and SR acknowledge funding through the FLIPPR project (www.flippr.at), as well as the “NAWI Graz” project by providing access to dcluster.tugraz.at. CK and CG acknowledge funding through the NanoSim project (http://www.sintef.no/projectweb/nanosim).

References
F.G. Fan and G. Ahmadi, "A Sublayer Model for Wall Deposition of Ellipsoidal Particles in Turbulent Streams," J. Aerosol Science 26:813-840 (1995).