Abstract

Cohesive sediments, such as mud, are observed in various marine and riverine environments, and the ability to model the dynamics of these sediments plays an important role in various applications in geomorphology, water resources, and environmental engineering. These types of sediments comprise very small particles that aggregate into bigger structures via cohesive forces and break up under external shear, a process that is commonly known as flocculation. Size class-based floc population models that rely on mass conservation and exchange between size classes via break-up and aggregation have been developed with the aid of experimental data. Such models yield promising results to describe flocculation in idealized experimental setups under various flow conditions, but more highly resolved simulation data is needed to validate their use. The key advantage of such simulations is that the primary particle properties and the flow conditions can be rigorously defined. In the present study, we apply a population balance equation (PBE) model to numerical simulation results of flocculation generated in isotropic turbulence. The numerical Confidential manuscript submitted to replace this text with title of book 2 simulations resolve even the smallest scales of turbulence in a 3D domain, where it is also possible to track particle positions and velocities in space and time. We compare key parameters of the PBE model, including the fractal dimension, the collision efficiency and the fragmentation rate, with different primary particles used in the numerical simulations. We show that the PBE model is able to predict the flocculation dynamics of the numerical simulations for moderate shear rates and sufficient cohesion between the particles. However, the analysis shows limitations of the PBE models when it comes to modelling the population of flocs with a low tendency to aggregate.