Numerical Simulation and Validation of Turbulent

A numerical investigation into the particle-turbulence interaction behaviour of dilute gas-particle flows over a backward-facing step geometry is reported. An Eulerian two-fluid model with additional turbulence transport equations for particles is employed. RNG based k-ε model is used as the turbulent closure wherein additional transport equations are solved to better represent the combined gas-particle interactions. Three different particle classes are considered and their streamwise velocities and fluctuations are compared against the experimental data of Fessler & Eaton (1995). INTRODUCTION Dilute two-phase flows are found to be critical part in many industrial and mining processes, such as pneumatic transporters, pulverized coal combustion equipments, spray drying, cooling and also sand blasting. Numerical simulations of these classes of particle-laden flows are complicated by the fact that in addition to the modeling of single-phase turbulence, special considerations should also be made to incorporate particle interaction with the primary turbulent flow field. In this paper, we present the results of the mean streamwise velocities; fluctuating velocities for both the carrier gas and particle phases, in addition particle number density (PND) results for different classes of particles considered are compared against the well established experimental data of Fessler and Eaton (1995). The re-attachment length for three particles along with two additional particles whose Stokes number is far less than other three has also been reported. GOVERNING EQUATIONS The Eulerian two-fluid model developed by Tu and Fletcher (1995) and Tu (1997) used in this study considers the gas and particle phases as two interpenetrating continua. Hereby, a two way coupling is achieved between the dispersed and the carrier phases. The underlying assumptions employed in the current study are: 1) The particulate phase is dilute and consists of mono disperse spherical particles. 2) For such a dilute flow, the gas volume fraction is approximated by unity. 3) The viscous stress and the pressure of the particulate phase are negligible. 4) The flow field is isothermal.