A porous medium is a region of a fluid continuum that also contains a solid material, with the interstitial spacing of the solid being too small to discretize with a mesh. Examples of porous media include filters, tube bundles, flow straighteners, sponges and radiators.
A porous medium provides a flow resistance that is manifested as a directional pressure drop. This pressure drop is a linear or non-linear function of the local flow velocity. In STAR-CCM+, these effects are accounted for in porous regions by including source terms in the momentum equations as detailed in the formulation below.