MODELING OF SALTATION AND TURBULENCE EFFECTS IN A HORIZONTAL GAS-SOLID BOUNDARY LAYER

ABSTRACT

This work is devoted to the study of the behavior of solid particles in a horizontal air boundary layer. A two-fluid model is selected to analyze the particle motion in the mixed regime where both saltation and turbulence effects are important. Boundary layer approximations are applied to the solid phase equations, using conventional space/time averaging. Resulting equations are shown to be in agreement with the phase averaged equations generally used in two-fluid models. Closure is achieved by means of a gradient law, however the particle diffusion and momentum transfer coefficients are distinguished using a variable particle Schmidt number. Turbulent particle diffusion is modeled using an available analytical model, which is modified to take the saltation effect into account in the particle r.m.s. velocity. Comparison between experimental and numerical results shows that the following analysis is acceptable within the experimental and numerical error. The model slightly underestimates the particle mean velocity in the outer region of the boundary layer, but yields satisfactory values of mass fluxes. The present simple approach adequately describes the particle behavior in a horizontal turbulent boundary layer, with the main originality being the realistic dependence of the particle Schmidt number upon the saltation phenomenon.