Settling of cohesive sediment: particle-resolved simulations

Abstract

We develop a physical and computational model for performing fully coupled, particle-resolved Direct Numerical Simulations of cohesive sediment, based on the Immersed Boundary Method. The model distributes the cohesive forces over a thin shell surrounding each particle, thereby allowing for the spatial and temporal resolution of the cohesive forces during particle-particle interactions. The influence of the cohesive forces is captured by a single dimensionless parameter in the form of a cohesion number, which represents the ratio of cohesive and gravitational forces acting on a particle. We test and validate the cohesive force model for binary particle interactions in the Drafting-Kissing-Tumbling (DKT) configuration. The DKT simulations demonstrate that cohesive particle pairs settle in a preferred orientation, with particles of very different sizes preferentially aligning themselves in the vertical direction, so that the smaller particle is drafted in the wake of the larger one. To test this mechanism in a system of higher complexity, we perform large simulations of 1,261 polydisperse settling particles starting from rest. These simulations reproduce several earlier experimental observations by other authors, such as the accelerated settling of sand and silt particles due to particle bonding. The simulations demonstrate that cohesive forces accelerate the overall settling process primarily because smaller grains attach to larger ones and settle in their wakes. For the present cohesion number values, we observe that settling can be accelerated by up to 29%. We propose physically based parametrization of classical hindered settling functions proposed by earlier authors, in order to account for cohesive forces. An investigation of the energy budget shows that the work of the collision forces can substantially modify the relevant energy conversion processes.

arXiv comment39 pages

References in corpus (5)

• Novel type of phase transition in a system of self-driven particles
• An Immersed Boundary Method with Direct Forcing for the Simulation of Particulate Flows
• Shear thickening, frictionless and frictional rheologies in non-Brownian suspensions
• A collision model for grain-resolving simulations of flows over dense, mobile, polydisperse granular sediment beds
• Investigating the Settling Dynamics of Cohesive Silt Particles With Particle-Resolving Simulations

Cited by in corpus (6)

• Confronting Grand Challenges in Environmental Fluid Mechanics
• Flocculation of suspended cohesive particles in homogeneous isotropic turbulence
• An efficient cellular flow model for cohesive particle flocculation in turbulence
• Rheology of mobile sediment beds in laminar shear flow: effects of creep and polydispersity
• Multi-fidelity uncertainty quantification of particle deposition in turbulent pipe flow
• Efficient methods for particle-resolved direct numerical simulation