A New Boundary Scheme for BGK Model
  In this paper, we proposed a new boundary condition scheme for the BGK model which has second order accuracy and can be developed to higher accuracy. Numerical tests show that the numerical solutions of the BGK model applied to the new boundary scheme have great agreement with analytical solutions. It is also found that the numerical accuracy of the present schemes is much better than that of the original extrapolation schemes proposed by Guo et al at small grid. 
Wang Peng and Zhang Shiqing
math.NA