A scaling analysis for point-particle approaches to turbulent multiphase flows

Simple dimensional arguments are used in establishing three different regimes of particle time scale, where explicit expression for particle Reynolds number and Stokes number are obtained as a function of nondimensional particle size (d/eta) and density ratio. From a comparative analysis of the different computational approaches available for turbulent multiphase flows it is argued that the point-particle approach is uniquely suited to address turbulent multiphase flows where the Stokes number, defined as the ratio of particle time scale to Kolmogorov time scale (tau(p)/tau(k)), is greater than 1. The Stokes number estimate has been used to establish parameter range where point-particle approach is ideally suited. The point-particle approach can be extended to handle "finite-sized" particles whose diameter approach that of the smallest resolved eddies. However, new challenges arise in the implementation of Lagrangian-Eulerian coupling between the particles and the carrier phase. An approach where the inter-phase momentum and energy coupling can be separated into a deterministic and a stochastic contribution has been suggested. (C) 2009 Elsevier Ltd. All rights reserved.