On the Effects of Anisotropy on the Flocculation of Cohesive Particles in Turbulence

Particle-resolved direct numerical simulations of finite-sized cohesive particles suspended in a turbulent channel flow are performed to study the effects of an anisotropic flow field on the aggregation, breakup, and restructuring of cohesive particles, known as flocculation. The strength of the cohesive force, and the density ratio between particle and fluid are varied. Consistent with findings in simplified cellular flows \cite{zhao_efficient_2020} and homogeneous isotropic turbulence \cite{zhao_HIT_2021}, the evolution of floc morphology through an initial aggregation-dominated transient is well modeled by an exponential. The flocculation rate and amplitude of relaxation of the floc morphology metrics, averaged over all flocs, are found to follow power law relations with $St$ and $Co$. The channel is binned and a similar analysis performed on the time evolution of locally-binned average floc sizes. Doing so reveals the dependence on the wall-normal direction of the flocculation rate and relaxation amplitude. Scaling the local flocculation parameters with their bulk values results in a collapse, suggesting that $St$ and $Co$ globally modify the flocculation dynamics. Finally, the flocculation rate associated with the exponential rate of decay is found to correlate directly with the wall-normal profile of mean shear.