Direct numerical simulation of particle pore-scale transport through three-dimensional porous media with arbitrarily polyhedral mesh

A new direct numerical simulation algorithm is developed for particle pore-scale transport through the porous media with arbitrarily polyhedral mesh. In the algorithm, the Navier-Stokes Equation is used to describe the continuous phase motion in the Eulerian framework; Newton's Second Law is used to describe the particle dynamics in the Lagrangian framework; Discrete element method is used to describe the particle-particle interactions and particle-wall interactions; RIGID is used to detect the contact state between particles with arbitrarily shaped pore walls. To suppress the spurious force oscillations (SFO) and improve the numerical accuracy of the evaluation of fluid-particle interaction, a novel consistent fictitious domain method (CFDM) in the arbitrarily collocated polyhedral mesh is developed. Numerical results of six test cases show that CFDM is accurate and second order in space, and no obvious SFO is found. Finally, the new direct numerical simulation algorithm is used to simulate the particle transport through three-dimensional porous media reconstructed from micro-CT scans from a real rock. The numerical results of a serial of tests with different particle sizes reveal several distinct microscopic flow mechanisms and the corresponding macroscopic characteristics. The change of channel resistance leads to the formation of particle motion paths in succession; Along a certain motion path, the particle moving velocity can be different at different sites; With the increase of particle size, the particle average retention time and particle average transit time increase; Particle velocity presents lognormal distribution, which becomes wider with the increase of particle size. The newly developed algorithm can be adopted as a direct numerical simulation tool to simulate particle motion in arbitrarily complex pore space.