Jet-noise has eventually been reduced to a minimum, but still there are problems in keeping the overall noise levels low during take-off and approach. The reason for this is basically that fan-noise, i.e. pressure fluctuations generated in the compressor or turbine, becomes dominating. This phenomenon can be recognized as non-linear and complex aerodynamics rather than acoustic problem in nature, and thus it becomes difficult to obtain models that are general and accurate. However, with the aid of CFD, the problem can now be studied in detail, but unfortunately this requires a very large number of points per wavelength to distinguish the wave solution from numerical errors. Applying the well-established linear methods for aeroacoustics in a parallel wall-duct to the fan stage, one can obtain analytical expressions for the dispersion-relation. A sinusoidal acoustic wave with the known dispersion-relation is then propagated thru a 2D numerical fan stage using a time-dependent finite-volume scheme. The numerical solution is then compared with the original wave to identify deviations that could originate from dispersion, dissipation and reflections induced by the numerical boundaries. An optimal number of points per wavelength were not established exactly, but in order to have good results within reasonable computational time a rough estimate of around 20 - 40 points per circumferential wavelength has shown to be sufficient to preserve the wave. In addition, certain physical and numerical phenomena applied to aeroacoustics has been more clarified, that includes; viscous interaction, numerical dispersion and dissipation of the sound waves, dependence of number of time steps per period, influence of different grid skew angles, and the errors induced by improper boundary conditions.