Particle dispersion and deposition in wall-bounded turbulent flow

Abstract

Particle dispersion and deposition in a fully developed turbulent channel flow at a friction Reynolds number of Reτ=180 for a wide range of Stokes numbers (St = 1-130) are investigated using the direct numerical simulation (DNS). The combined effect of gravity and the Saffman lift force on the particle deposition velocities in upward and downward flows are considered. The results are compared with recent experimental measurements and numerical benchmark solutions. For particle–wall collisions, two scenarios of fully elastic and no-rebound (trap-wall) collisions are considered. Due to the turbophoresis effect and the steady migration of particles toward the walls, a stationary state cannot be reached for particle concentration with the fully elastic assumption. To alleviate this problem, for every particle that impacts the wall a new particle is added to the computational domain with the trap-wall assumption. The stationary particle field is further time-averaged to present the average particle velocities, particle concentrations, and particle velocity fluctuations profiles. It is shown that at lower Stokes numbers, the deposition velocity of downward channel flow is higher than the upward flow, whereas at higher Stokes numbers the upward flow has a higher deposition rate but a lower near-wall particle concentration. This higher deposition rate is attributed to the combined effect of gravity and the positive Saffman lift force that brings the inactive particles trapped in the viscous sublayer to the buffer layer, resulting in an increase of their wall-normal turbulent fluctuations and their wall-collision rates.