Flow simulations in nano-channel by lattice Boltzmann method

For the lower-cost flow simulations through nano-sized porous media such as catalyst layer of fuel cell, lattice Boltzmann method (LBM) has been improved for high Knudsen number flows by considering diffuse scattering boundary condition and effective relaxation time related to Knudsen number. However, effect of the discrete velocity model has not been validated and only simple geometries are examined for validation of the computational scheme. In this paper, the applicability of the D2Q9 microflow LBM is investigated. It is found that for a channel flow, D2Q9 model shows the tendency of the high-Knudsen number flow with lower slip velocity compared to that by D2Q21 model. Next, the LBM simulations are applied to the flow inside a nano-channel with square cylinder. The reasonable velocity profiles are obtained at D2Q9 rather than D2Q21 model, which suggests that the difference in equivalent distribution function for Q9 and Q21 does not affect drastically for the nano-scale complex flow.