Flocculation and Breakup of Finite-Sized Cohesive Particles in a Turbulent Channel Flow*

We present a computational study of the flocculation dynamics and turbulence modulation in a channel flow laden with small, finite size, cohesive particles. We conduct a series of four-way coupled, grain-resolved direct numerical simulations, across which the strength of the cohesive force and particle inertia (density) are varied in the absence of gravity. The strength of cohesion is shown to govern the size (Ο(1-100) particle diameters) and number of aggregates. Interestingly, despite the prevalence of shear-induced migration at higher particle Stokes numbers, the maximum floc size is shown to be insensitive to the particle density. We additionally analyze floc properties such as size, shape, and lifespan as a function of the wall normal distance. The higher mean velocity gradient and turbulent activity near the wall is found to both facilitate aggregation by bringing particles together, while also prompting breakup. Enabled by the fully coupled nature of the simulations, we quantify the effect of aggregation on the turbulence by reporting classical first and second order turbulence statistics for both the fluid and particles. Finally, the role of volume fraction and turbulence intensity on the flocculation process are briefly discussed.