  In this study a new type of non-reflective boundary condition (NRBC) for the
Lattice Boltzmann Method (LBM) is proposed; the Non-equilibrium Symmetry
Boundary Condition (NSBC). The idea behind this boundary condition is to
utilize the characteristics of the non-equilibrium distribution function to
assign values to the incoming populations. A simple gradient based
extrapolation technique and a far-field criterion are used to predict the
macroscopic fluid variables. To demonstrate the non-reflective behaviour of the
NSBC, two different tests have been carried out, examining the capability of
the boundary to absorb acoustic waves respectively vortices. The results for
both tests show that the amount of reflection generated by the NSBC is nearly
zero.
