A sinusoidal acoustic wave with known dispersion-relation was propagated through a two-dimensional duct using a finite-volume scheme
showing that a rough estimate of around 40 points per wavelength under second order accuracy was sufficient to preserve the wave.Adding an extended coarse grid out of the computational region could reduce the unwanted boundary reflection.A guideline of the extended- grids length and axial size for the good effect of absorbing the boundary reflection with less computation was provided.