Particle deposition in turbulent duct flows

Abstract

Particle deposition in fully developed turbulent square duct flows is simulated using large eddy simulation for Reynolds numbers, based on the bulk velocity and duct width, equal to 250k, 83k and 10,320. A particle equation of motion including Stokes drag, lift, buoyancy and gravitational forces is used for particle trajectory analysis. Results obtained for the fluid phase show good agreement with experimental data and the predictions of direct numerical simulations. Predictions for particles show that the secondary flow established in the duct cross-section plays an important role in the particle deposition process. Under the influence of this flow, high-inertia particles (particle Stokes number, St>12.38) tend to deposit close to the corners of the duct floor, while low-inertia particles (St<6.43) deposit near the floor centre. It is shown that the flow Reynolds number, particle size, drag force, shear-induced lift force and gravity all affect the particle deposition process. Particle deposition in the vertical direction increases with flow Reynolds number but simultaneously decreases in the horizontal direction. The particle deposition velocity is found to increase with both the particle size and the flow Reynolds number, with the tendency for deposition at the duct corners increasing with both variables. From a dynamic analysis, gravity most significantly affects particle deposition in the vertical direction, while in the horizontal direction the drag force dominates. The influence of the lift force increases with particle size, and its effect becomes significant as particles approach the duct floor; hence, it can act as another important factor causing particles to accumulate at the corners of the duct. Generally, and for all particle populations in the three flows considered, the particle deposition process can be described by the free-flight model.