Lattice-gas simulations of two-phase flow in porous media

Nearly all CFD-methods can be considered as discretization methods for partial differential equations, such as finite difference, finite volume, finite element, spectral or boundary integral element methods. Virtually unrecognized by the scientific mainstream in CFD, during the last decade, a completely different approach to flow simulation has been developed in Computational Physics. The basic idea of Lattice-Gas Solvers (LGS) goes back to the Cellular Automaton concept of John von Neumann. LGS use objects ('cells') being extremely simple compared to finite boxes or finite elements. The state of a cell is usually described by only a few bits. Therefore often two orders of magnitude more cells are used for a simulation with LGS than 'elements' in a finite element computation. LGS are explicit time stepping procedures; no equation systems have to be solved. Thus every timestep is extremely cheap in terms of CPU power compared to standard procedures, yet again much shorter time steps have to be used. LGS are inherently parallel, being suitable to coarse grain as well as to fine grain parallelization. The paper will discuss some advantages and disadvantages of Lattice-Gas Solvers and present LG simulation results of two-phase flow with moving boundaries on a microscopic scale for a two-dimensional test geometry of randomly distributed equally-sized disks where the effect of surface tension on the steady-state saturation will be demonstrated.