LBM-DEM simulation of fluid-solid interaction in porous media

Particulate flow arises in many engineering applications, for example, debris flow, sand production, soil erosion and so on. In this research topic, a numerical method called LBM-DEM is proposed to investigate the problem of complex particle laden flows.
The behavior of particles are simulated by the discrete element method (DEM). DEM is a finite-size particle method, where the shape and size of each particle are considered. The behaviors of particles are governed by the fundamental Newton’s second law. The particular feature of DEM reveals the discrete nature of geomaterials that allows fracturing, transport and large displacement at the failure state.
Generally, the motion of fluid can be described by three types of mathematical models according to the observed scales, referring to microscopic models at molecular scale, kinetic theories at mesoscopic scale, and continuum models at macroscopic scale.
The lattice Boltzmann method (LBM) is adopted to simulate the motion of fluids. LBM describes the fluid motion at the mesoscopic scale based on the kinetic theory. Compared to molecular dynamics (MD), both LBM and MD observe the fluid motion at rather small scale so that the information about molecules can be revealed. However, MD focuses on the behavior of each molecule and LBM describes the statistical behavior of molecules. By this way, the computational cost is much smaller for LBM. Compared to continuum models, LBM is not limited by the assumption of continuity. Besides, details of the local fluid motion can be captured by LBM.
The fluid-particle interaction is described by coupling between LBM and DEM. The particle surface is treated as a boundary immersed in the fluid on which a suitable boundary condition is imposed. In this approach, the translation motion and rotation of each particle are both tracked, where the hydrodynamic force and torque exerted on the particle by the fluid are obtained from the particle-fluid boundary condition. Furthermore, by using the LBM-DEM coupling method the details of the flow around the particles can also be captured, which is important in the study of the fundamental mechanisms in particulate flows.
For this review period, the following tasks have been accomplished:
1. Literature review of the particulate flow problems, including sand production, incipient motion and debris flow;
2. Understand the basic principle of LBM and DEM;
3. Build up the computer code for LBM-DEM coupling method;
4. Verify the numerical code by simulation of simple well known fluid-particle interaction problems, including drag force acting on a particle within a Poiseuille flow, single particle sedimentation test, and drafting-kissing-tumbling (DGK) of two settling particles.