An improved model for anisotropic dispersion of small particles in turbulent shear flows

In order to investigate the dispersion of small particles in a turbulent shear flow, a new model based on accurate modelling of the directional dependence of the fluid Lagrangian time scales is proposed and tested against experimental data in a gas-solid channel flow. The continuum phase is described by a nonlinear low-Reynolds kappa-epsilon model, thus allowing a fine description of turbulence anisotropy and near-wall effects. The dispersed phase is described by a Lagrangian stochastic method, which is formulated in order to take into account the nonhomogeneity and the anisotropy of turbulence. The fluid Lagrangian time scales in each direction are assessed following a recent proposal supported by channel flow DNS computations. The integral time scales of the fluid seen by the particles are then estimated in taking the inertia and crossing trajectory effects into account. The numerical predictions (particle and fluid statistical quantities) obtained by means of this time scale model and previously available time scale models are compared and confronted to recent experimental data from the literature about the motion of small solid particles in a turbulent vertical channel flow. It is shown that the new Lagrangian time scale formulation leads to very satisfactory results compared to the measurements.