Modelling flocculation using CFD-DEM in a turbulent flow, with reference to “Particle flocculation in a stirred tank: A microscopic test by coupled CFD-DEM approach” by Wang et al.

Abstract

The coupled Computational Fluid Dynamics – Discrete Element Method (CFD-DEM) modelling technique is a potentially very powerful one for simulating the flocculation process (as well as many other coupled particulate-fluid flow phenomena). However, great care must be used when the fluid flow is turbulent, since RANS (Reynolds averaged Navier-Stokes) turbulence models cannot be used for the CFD part of the simulation since they are incompatible with the DEM component of the model. This is because DEM simulation requires the instantaneous fluid velocity to be available at each particle location at each time-step, and this information is not given by a RANS CFD simulation. A recent example is given of this erroneous simulation technique, together with examples of more rigorous alternative methods.