  Modeling coupled systems of free flow adjacent to a porous medium by means of
fully resolved Navier-Stokes equations is limited by the immense computational
cost and is thus only feasible for relatively small domains. Model reduction
allows to decrease a model's complexity while maintaining an acceptable degree
of accuracy. Starting from a fully resolved three-dimensional numerical model,
which is compared to high-resolution micro-PIV experimental data obtained from
a previous study (Terzis et al.,2019), we perform a two-fold model reduction:
first, a quasi-3D model incorporating a wall friction term is successfully
compared to the fully resolved model. Second, we employ a pore-network model to
account for the porous part of the domain and couple it to the quasi-3D model
which still resolves the free-flow part of the domain (Weishaupt et al., 2019).
We have extended this coupling approach here to include slip velocities at the
pore throats intersecting with the free-flow domain. The proposed method is
simple, accurate and comes at no additional run-time penalty. The coupled model
deviates by less than 10 % from the other two model concepts. Several hours of
run-time was required for the three-dimensional model compared to eleven and
five minutes necessary for the quasi-3D and coupled model which highlights the
benefits of model reduction.
