A Numerical Investigation of Particle Deposition on a Square Cylinder Placed in a Channel Flow

Abstract

Particle deposition on a square cylinder placed in a rectangular channel was investigated for unsteady vortical flows. For the two-phase flow simulations, the unsteady gas flow field was computed by solving the incompressible Navier-Stokes equations using a staggered-grid control volume approach and the Marker-and-Cell (MAC) technique. The particle dynamics were simulated using the modified Basset-Bousinesq-Oseen (BBO) equation. The gas-phase algorithm was validated using four test problems involving both steady and unsteady flows. Numerical experiments were also conducted to evaluate the relative contributions of various terms in the BBO equation. For particle dynamics in unsteady vortical flows, all the secondary terms were found to be negligible compared to the steady state viscous term at particle density ratios >20. The two-phase flow model and the detailed flow visualization were then employed to characterize particle dispersion and deposition as a function of the Reynolds number, particle Stokes number (St), and density ratio (e). Particle dispersion in the cylinder wake exhibited a typical nonmonotonic behavior. Particles with St 1.0 were essentially unaffected by the flow in the near wake region. In addition, the small St particles were distributed in the vortex core, while the intermediate St particles were distributed around the vortex periphery. For e > 20, the particle deposition was essentially characterized by the Stokes number. The amount of deposition increased precipitously as St was increased from zero to unity, then increased slowly for St between 1 to 3, and was essentially independent of St for St > 3.0. For the range of Reynolds numbers investigated, which included both laminar and transitional regimes, the Reynolds number (Re) had a negligible effect on particle deposition, but a more discernible effect on particle distribution and dispersion.