  Drops on a free-flow/porous-medium-flow interface have a strong influence on
the exchange of mass, momentum and energy between the two macroscopic flow
regimes. Modeling droplet-related pore-scale processes in a macro-scale context
is challenging due to the scale gap, but might be rewarding due to relatively
low computational costs. We develop a three-domain approach to model drop
formation, growth, detachment and film flow in a lower-dimensional interface
domain. A simple upscaling technique allows to compute the drop-covered
interface area fraction which affects the coupling fluxes. In a first scenario,
only drop formation, growth and detachment are taken into account. Then,
spreading and merging due to lateral fluxes are considered as well. The
simulation results show that the impact of these droplet-related processes can
be captured. However, extensions are necessary to represent the influence on
the free flow more precisely.
