Preventing wall deposition in duct flows: The role of particle number density and flow direction

Abstract Particle deposition in wall‐bounded turbulent flows is a challenge in many industries, including pneumatic conveying, filtration, and related applications. When particles accumulate near boundaries, they reduce transport efficiency, alter near‐wall flow structures, and cause blockage. Although particle deposition has been studied extensively, the mechanisms that govern near‐wall accumulation remain unclear when several effects act simultaneously. In particular, the combined influence of flow direction, particle number density, and Stokes number has not been fully resolved when gravity, Saffman lift, and particle–particle collisions are all present. In this study, we perform direct numerical simulations of particle‐laden turbulent flow in a square duct. The fluid phase is resolved in an Eulerian framework, while the particle phase is tracked in a Lagrangian framework using a point‐particle approach. We studied six cases, three with downward flow and three with upward flow, each with a different particle number density. Results show that particle deposition at the walls decreases when particles lag the fluid, as in upward flows. For and a particle number density of , the wall particle concentration decreased by a factor of 85 in upward flow compared to downward flow. In downward flows, doubling the particle number doubles the particle–particle collision rate and reduces the wall concentration by a factor of six. In upward flows, particle number density has little influence on the concentration profiles. The findings can help identify flow conditions that prevent particle deposition.