Porous media
In a model of porous media, the fluid domain has a certain permeability described by a permeability matrix K, which prescribes a permeability which can be different in each flow direction. In the simplest case K is a scalar, corresponding to an isotropic permeability in all directions.
In the course GitHub repo, a template file is added which implements a Navier-Stokes-Brinkman model for porous media:
Navier-Stokes-Brinkman equations, FEniCS Jupiter notebook (GitHub) Links to an external site.
To read more about the model, see e.g.