Direct numerical simulation of particle wall transfer and deposition in upward turbulent pipe flow

Abstract

Transfer and deposition of inertial particles or droplets in turbulent pipe flow are crucial processes in a number of industrial and environmental applications. In this work, we use direct numerical simulation (DNS) and Lagrangian tracking to study turbulent transfer and deposition of inertial particles in vertical upward circular pipe flow. Our objects are: (i) to quantify turbulent transfer of heavy particles to the wall and away from the wall; (ii) to examine the connection between particle transfer mechanisms and turbulence structure in the boundary layer. We use a finite difference DNS to compute the three-dimensional time dependent turbulent flow field ( Re τ =337) and Lagrangian tracking of a dilute dispersion of heavy particles––flyashes in air––to simulate the dynamics of particles. Drag, lift and gravity are used in the equation of motion for the particles, which are assumed to have no influence on the flow field. Particle interaction with the wall is fully elastic. Results on preferential distribution of particles in the boundary layer, particle fluxes to and off the wall and particle deposition mechanisms are shown. Our findings confirm: (i) the specific tendency of particles to segregate in the near-wall region; (ii) the crucial role of the instantaneous realizations of the Reynolds stresses in determining particle fluxes toward and away from the wall; (iii) the relative importance of free-flight and diffusion deposition mechanisms.