Preferential concentration of particles in a fully developed turbulent square duct flow

Abstract

The preferential concentration of dense particles in a downward, fully developed turbulent square duct flow at Re τ =360, based on mean friction velocity and duct width, is studied using large eddy simulations. Due to the low volume fractions involved (maximum volume fraction <10 −5), one-way coupled simulations are performed, i.e., two-way coupling and particle–particle collisions are not considered. The continuous and the dispersed phases are treated using Eulerian and Lagrangian approaches, respectively. A finite volume based second-order accurate fractional step scheme is used to integrate the unsteady, three-dimensional Navier–Stokes equations. The subgrid stresses are modeled with a dynamic subgrid kinetic energy model, as reported previously. The particle equation of motion includes drag, lift and gravity forces and is integrated using the fourth-order accurate Runge–Kutta method. Four cross-sectional locations representative of the mean secondary flow patterns and six particle response times were chosen to study the effect of location and particle inertia on preferential concentration. To demonstrate preferential concentration, variation of vorticity magnitude, swirling strength, maximum compressional strain-rate, and ∇ u : ∇ u , and their probability distribution functions (PDF) conditioned on particle presence, with particle response time is presented. Since the square duct cross-section is inhomogeneous, we also study variation in preferential concentration with cross-sectional location. Particles are seen to accumulate in regions of high ∇ u : ∇ u and strain-rate and in regions of low swirling strength. In general, particles accumulate in regions of low vorticity magnitude. However, near the wall, the tendency of particles to accumulate in regions of high vorticity increases with response time.