Secondary flow-induced particle dynamics in fully developed turbulent square ducts with a free-slip boundary

Secondary flow effects on particle dynamics are investigated in a fully developed turbulent open square duct flow at a shear Reynolds number of Reτ = 300. The modelling of the fluid phase is based on direct numerical simulation, and the trajectories of particles are described using a one-way coupled Lagrangian particle tracking technique, with shear Stokes numbers ranging from St+ = 0.31–260. The results obtained show that particles with St+ ≥ 25 accumulate strongly in the lower corners of the duct, while the upper corners with mixed boundaries are relatively devoid of particles. The transverse cross-stream velocities for all considered particle sets exceed those of the fluid phase near the intersection of the inner and outer secondary vortices. Furthermore, the cross-sectional secondary flow is observed to encourage particle acceleration near the free surface. A further in-depth analysis regarding the impact of various hydrodynamic forces exerted on the particles in the duct cross-section is also provided.