Construction of a LBM-DEM Coupling System and its Applications in Modeling Fluid Particle Interaction in Porous Media Flow.

摘要

The problem of fluid flow through porous media may be viewed as a two-phase system, i.e., the solid grain skeleton and the pore space, filled with stationary or moving fluids (e.g., air, gas, water, oil, etc). Most porous media flow problems may be reasonably described by a poro-mechanical theory formulated within the framework of a continuum at the macro-scale. However, for the problems such as oil-well sand-production in which the interfacial physics along the solid-fluid interface dominates the performance of the system, the macroscopic averaging method employed in continuum models is not able to catch the primary physical processes due to its low resolution and inability in handling collapsed solid matrix. To capture fluid-solid interaction at the local scale, the grains in the solid skeleton have to be modeled explicitly and the fluid flow in the pore space needs to be simulated at a resolution finer than that of pores and grains.;In this study, the solid skeleton is represented by the assembly of particulate distinct elements in the commercial distinct element method (DEM) code PFC; the pore-scale fluid flow is modeled by the lattice Boltzmann method (LBM); an immersed boundary scheme is employed to handle the interaction at the fluid-particle interface. The LBM is implemented in PFC and coupled with the existing DEM scheme. The accuracy of the LBM and LBM-PFC coupling is verified with a number of classic hydrodynamic (i.e., Poiseuille channel flow, lid-driven cavity flow, duct flow, Stokes's first and second problems) and fluid-particle interaction (i.e., fluid flow over fixed cylinder in channel flow, Taylor Couette flow, particle settling inside tube, fluid flow over fixed sphere in channel flow) problems for which the analytical solutions are available for comparison.;The verified LBM-DEM coupling system is then applied to study three types of problems of fluid solid interaction or fluid flow in porous media. In the first type, two porous media flow problems with known analytical solutions, i.e., creeping flow in periodic pore and upward seepage flow through a single column of spherical particles, are simulated in LBM-PFC system. In the simulation of creeping flow in periodic pore, the friction coefficients of flow through idealized porous media are measured for various solid volume fractions and compared with the corresponding analytical solutions. In the upward seepage flow simulation, the fluid drag forces on the grains, the seepage induced deformation of the solid matrix and pore pressure development and distribution in the pore space are monitored and compared with the analytical solutions. In the second type, three widely utilized empirical laws describing porous media flow, i.e., Darcy's law, Carman-Kozeny relation and Ergun equation, are tested. The numerical simulations show that the fundamental macroscopic physical laws in general porous media flow can be well recovered in this system. In the third type, the developed coupling system is used as a virtual laboratory to experiment two laboratory observations. The first simulation shows that the DKT (Drafting-Kissing-Tumbling) cycles of two particles settling inside fluid tank observed in physical laboratory can be repeated in the LBM-PFC coupling system. The second simulation reproduces the collapse and re-forming of sand arches in the perforation cavity under increasing fluid pressure gradient, as observed in the physical experiments.