3D Lattice Boltzmann Method-Discrete-Element Method with Immersed Moving Boundary Scheme Numerical Modeling of Microparticles Migration Carried by a Fluid in Fracture

Summary Based on the LBM-IMB-DEM (coupled lattice Boltzmann method-discrete-element method with immersed moving boundary scheme) model, the 3D microparticles’ migration carried by a fluid in fracture is numerically investigated both considering and not considering the van der Waals adhesive force. A boundary cells’ tracing method called the layer-by-layer tracing method both applicable to 2D and 3D situations for IMB with high efficiency and accuracy is proposed, and based on its searching results, the contacts in DEM could be detected straightforwardly with a finite amount of computation. In the layer-by-layer tracing method, a limited number of points, including some cell centers and nodes, near the particle boundary are determined whether they are covered by the particle, and then the other cells in one layer could be precisely classified. In the contact detecting process for DEM, based on the boundary cells tracing results in IMB, the cells that are covered by no less than two particles are the potential cells where there may be contacts. For wall boundaries with irregular shapes, the wall solid boundary (WSB) cells are converted to circumcircle (or circumscribed sphere in 3D situation), and then the solid particle-wall interactions could be replaced by the interactions between the solid particles and those circumcircles or circumscribed spheres. Two cases, including single-particle sedimentation in a viscous fluid, two-particle Drafting-Kissing-Tumbling (DKT) simulation for both nonadhesive and adhesive particles, are used to validate the LBM-IMB-DEM method. Besides, multiparticle sedimentation tests for different particle radiuses are conducted to present the advantages of the layer-by-layer tracing method. At last, nonadhesive and adhesive microparticles’ liberation, transport, and retention carried by a fluid in fracture with irregular shapes are simulated. The numerical results show that the adhesive force that plays a dominated role for microparticles has significant effects on the mechanics of solid particles migration. Under the influence of adhesive forces, the microparticles tend to form a stable agglomerate and migrate as a whole, which is different from the situation for nonadhesive particles where they are relatively independent and basically migrate by layer. Besides, even if the fluid velocity is much lower than the critical velocity evaluated through force or torque analysis on a single particle, when the total hydrodynamic forces exerted on the agglomerate overcome the total adhesive force between the wall and the lower layer of particles, the agglomerate can start to move and liberate from the wall.