Analysis of Simulation Data for Cohesive Sediment Flocculation Using a Population Balance Model

Cohesive sediments like mud, found in marine and river environments, are important for many aspects of water resource management and environmental engineering. These sediments consist of small particles that aggregate via cohesive forces and break apart under shear, a process called flocculation. Size-class-based population models, developed using experimental data, describe flocculation in a volume-averaged sense by considering mass conservation and the exchange of particles through breakup and aggregation. Although these models work well in controlled experimental conditions, more detailed data are needed for validation. Numerical simulations of sediment-laden flows allow for definition of particle properties and flow conditions to provide such data under precisely defined boundary conditions. This chapter applies a population balance equation (PBE) model to simulate results of flocculation in isotropic turbulence, resolving even the smallest turbulence scales in three dimensions. The positions and velocities of particles are tracked over time. Key PBE model parameters-fractal dimension, collision efficiency, and fragmentation rate-are compared with different primary particles used in the simulations. Results show that the PBE model can predict flocculation dynamics at moderate shear rates with sufficient particle cohesion. However, the analysis reveals limitations in modeling flocs with low aggregation tendencies.