Computational methods for pore-scale simulation of rarefied gas flow

Direct simulation at the pore-scale is crucial to unravel rarefaction effect on gas transport in tight porous media. To satisfy dual demands modeling accuracy and computation effort, an appropriate method must be chosen. This work, therefore, evaluates four numerical methods for rarefied flows a two-dimensional (2D) model media over wide range of rarefaction. These are incompressible Navier-Stokes equation with first-order velocity-slip boundary condition, three gas-kinetic solvers i.e. finite-difference (FD) iterative solver linearized Bhatnagar, Gross Crook (BGK) kinetic equation, finite-volume (FV) non-linear Shakhov model, open-source direct Monte Carlos (DSMC) solver. The benchmark cases cover characteristic Knudsen number ranging from 0.0231 4.62 while Reynolds numbers kept less than 1.0. All developed OpenFOAM, except FD solver, allowing us investigate local grid refinements using automatic Cartesian generator OpenFOAM. flow fields apparent permeabilities predicted by all have been compared detail. Besides, computational time these measured analyzed demonstrate relative cost solvers. It found that most efficient one gives accurate results whole number. Finally, this study also feasibility recently discrete unified scheme (DUGKS), algorithm aforementioned flow. agree well other two