  In this paper, a new formalism for the filtered density function (FDF)
approach is developed for the treatment of turbulent polydispersed two-phase
flows in LES simulations. Contrary to the FDF used for turbulent reactive
single-phase flows, the present formalislm is based on Lagrangian quantities
and, in particular, on the Lagrangian filtered mass density function (LFMDF) as
the central concept. This framework allows modeling and simulation of particle
flows for LES to be set in a rigorous context and various links with other
approaches to be made. In particular, the relation between LES for particle
simulations of single-phase flows and Smoothed Particle Hydrodynamics (SPH) is
put forward. Then, the discussion and derivation of possible subgrid stochastic
models used for Lagrangian models in two-phase flows can set in a clear
probabilistic equivalence with the corresponding LFMDF.
