LES of particle collision and agglomeration in vertical channel flows

Large eddy simulation in a four-way coupled system is used to simulate particle collisions and agglomeration in turbulent vertical channel flows. The particle phase is modelled using Lagrangian particle tracking, ensuring that individual particle behaviour is effectively monitored by solving the particle equation of motion. Particle collisions are described using the hard-sphere collision model, with agglomeration tested based on the pre-collision kinetic energy, restitution coefficient and the van der Waals interactions between particles. The conditions influencing collision and agglomeration are studied for a fluid of Re-tau = 300 with 125 mu m spherical particles at volume fraction phi(v) similar to O(10(-3)). Comparing flows in upward and downward directions reveals the influence of the various forces acting on the particles, with the drag and lift forces being dominant in both flows, although the latter is found to govern particle behaviour in downflow, driving the particles towards the wall regions where increased collisions and agglomeration occur. The particle distribution in upflow is more symmetric, with fewer collisions and agglomerations, due to the increased effects of drag. The fluid flow is also slightly modified by the presence of the particles.