Large-Eddy-Simulation Tools for Multiphase Flows

Multiphase flows occurring in nature and in technological applications are often turbulent. The large range of length scales and timescales in turbulent multiphase flows makes direct numerical simulation of the microscale governing equations intractable for many applications. In this article we review a systematic approach for developing large-eddy-simulation (LES) tools for dispersed multiphase flows starting from the microscale model. A key intermediate step is the mesoscopic model for the dispersed phase, formulated in terms of kinetic equations, that contains the physical models for the flow. Owing to the phase-space variables, direct solution of the mesoscopic model is usually intractable, and additional mathematical approximations are introduced to arrive at a macroscopic model. We show that self-conditioned LES models can be derived for both the mesoscopic and macroscopic models, but the former is preferred to ensure consistency and physical accuracy. The principal difficulties and open challenges in closing the LES model equations are highlighted.