In modelling of flow through porous media inertia-effects must sometimes be considered. This is often done by usage of the empirically derived Ergun equation that can describe the response of several porous media but does not reveal the real mechanisms for the flow. In order to increase the understanding of such flows we have therefore performed a micromechanically based study of moderate Re' flow between parallel cylinders using a Computational Fluid Dynamics approach. The simulations are carried out with quality and trust by using grid refinement techniques and securing that the iteration error is sufficiently small. Main results are that the Ergun equation fits well to simulated data up to Re' 20, that inertia-effects must be taken into account when Re' exceeds 10 and that results from stationary simulations replicate time resolved ones at least up to Re' 880.