Momentum transfer correction for macroscopic-gradient boundary conditions in lattice Boltzmann methods

The boundary conditions used to represent macroscopic-gradient-related effects in arbitrary geometries with the lattice Boltzmann methods need a trade-off between the complexity of the scheme, due to the loss of localness and the difficulties for directly applying link-based approaches, and the accuracy obtained. A generalization of the momentum transfer boundary condition is presented, in which the arbitrary location of the boundary is addressed with link-wise interpolation (used for Dirichlet conditions) and the macroscopic gradient is taken into account with a finite-difference scheme. This leads to a stable approach for arbitrary geometries that can be used to impose Neumann and Robin boundary conditions. The proposal is validated for stress boundary conditions at walls. Two-dimensional steady and unsteady configurations are used as test case: partial-slip flow between two infinite plates and the slip flow past a circular cylinder.