  Pressure (density) and velocity boundary conditions inside a flow domain are
studied for 2-D and 3-D lattice Boltzmann BGK models (LBGK) and new method to
specify these conditions are proposed. These conditions are consistent with the
boundary condition we proposed in a previous paper using an idea of bounce-back
of non-equilibrium distribution. These conditions give excellent results for
the regular LBGK models, and were shown to be second-order accurate by
numerical examples. When they are used together with the improved
incompressible LBGK model proposed by zou et al. the simulation results recover
the analytical solution of the plane Poiseuille flow driven by pressure
(density) difference with machine accuracy.
