Multiphase Eulerian simulations of a sedimentation process in a solid-fluid particle-laden flow

In this paper, modelling details have been investigated for a multiphase settling process in a two-dimensional particle-laden flow. Unsteady simulations have been performed by using an Eulerian-Eulerian multiphase approach. A preliminary mesh sensitivity study showed that the numerical results might become oscillatory when the grid spacing is comparable with the solid particle diameter, which indicates that excessive mesh refinement is undesirable. In these multiphase flows, the interaction between the fluid and solid phases is modelled relying on purely heuristic arguments, which is a major source of uncertainties. Therefore fluid-solid exchange and drag coefficient models have been compared and assessed in terms of their accuracy. Since the ANSYS-FLUENT commercial software package provides only a few of these approaches, the majority of the models have been implemented through User-Defined Functions (UDFs) in C programming language. The results showed that the choice of an exchange model has considerable impact on the solution and the best agreement has been achieved by employing the formulation proposed by Schiller and Naumann [8]. However, only minor differences have been experienced between the distinct drag models for this specific problem due to their similar behaviour over the investigated settling Reynolds number range.