Flocculation of suspended cohesive particles in Rayleigh-Bénard turbulence

We employ a four-way coupled numerical approach to investigate the dynamics of suspended cohesive particles in Rayleigh-Bénard turbulence. The Stokes drag, cohesive, and direct contact forces between primary particles are captured in detail, yielding the phenomena of flocs' aggregation, breakage, and deformation. The momentum and thermal exchange between primary particles and the fluid are considered based on the Source-in-Cell method. We found that the initial increase of the average floc size indicates a temporary flocculation phase, which is followed by an equilibrium phase where the average floc size becomes stable, reflecting the balance between aggregation and breakage. Different from the traditional perspective, which attributed the local accumulation of particles to their gravity, we found that the suspended particles still tend to accumulate in the bottom hot boundary layer region. This accumulation is primarily driven by the temperature-induced variation in aggregation strength and the nonuniform spatial distribution of floc inertia. Additionally, the stronger cohesion yields a reduction in momentum intensity of the thermal plumes, primarily due to the more pronounced weakening of fluid momentum by the larger flocs.