Abstract
Coupled large eddy simulation and the discrete element method are applied to study turbulent particle–laden flows, including particle dispersion and agglomeration, in a channel. The particle–particle interaction model is based on the Hertz–Mindlin approach with Johnson–Kendall–Roberts cohesion to allow the simulation of van der Waals forces in a dry air flow. The influence of different particle surface energies, and the impact of fluid turbulence, on agglomeration behaviour are investigated. The agglomeration rate is found to be strongly influenced by the particle surface energy, with a positive relationship observed between the two. Particle agglomeration is found to be enhanced in two separate regions within the channel. First, in the near-wall region due to the high particle concentration there driven by turbophoresis, and secondly in the buffer region where the high turbulence intensity enhances particle–particle interactions.
Highlights
Understanding the fundamental aspects of turbulent fluid–particle flows is of relevance to processes employed in a wide range of applications, such as oil and gas flow assurance in pipes, powder dispersion from dry powder inhalers and particle re-suspension in nuclear waste ponds
large eddy simulation (LES) is coupled with the discrete element method to provide further understanding of particle–laden flows, in particular in relation to how particles interact in a turbulent channel flow, and how those interactions result in the formation of agglomerates which affect the dispersion and deposition of the particles within the flow
The length of the channel in the streamwise direction was sufficiently long to capture the streamwise-elongated, near-wall turbulent structures that exist in wall-bounded shear flows; such structures are usually shorter than ∼1000 wall units (Robinson, 1991)
Summary
Understanding the fundamental aspects of turbulent fluid–particle flows is of relevance to processes employed in a wide range of applications, such as oil and gas flow assurance in pipes, powder dispersion from dry powder inhalers and particle re-suspension in nuclear waste ponds. The particle velocity is almost invariable throughout the plug, the relative slip velocity of particles in the near-wall region is large These characteristics have been studied using computational fluid dynamic (CFD) approaches coupled to the discrete element (DEM) method by a number of authors (Tsuji et al, 1992; Xiang and McGlinchey, 2004; Li and Kuipers, 2005; Li and Mason, 2000; Lim et al, 2006a,b; Fraige and Langston, 2006; Zhang and Thornton, 2007; Kuang et al, 2008; Chu and Yu, 2008). LES is coupled with the discrete element method to provide further understanding of particle–laden flows, in particular in relation to how particles interact in a turbulent channel flow, and how those interactions result in the formation of agglomerates which affect the dispersion and deposition of the particles within the flow
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