  The effect of a network of fixed rigid fibers on fluid flow is investigated
by means of three-dimensional direct numerical simulations using an immersed
boundary method for the fluid-structure coupling. Different flows are
considered (i.e., cellular, parallel and homogeneous isotropic turbulent flow)
in order to identify the modification of the classic energy budget occurring
within canopies or fibrous media, as well as particle-laden flows. First, we
investigate the stabilizing effect of the network on the
Arnold-Beltrami-Childress (ABC) cellular flow, showing that, the steady
configuration obtained for a sufficiently large fiber concentration mimics the
single-phase stable solution at a lower Reynolds number. Focusing on the
large-scale dynamics, the effect of the drag exerted by the network on the flow
can be effectively modelled by means of a Darcy's friction term. For the
latter, we propose a phenomenological expression that is corroborated when
extending our analysis to the Kolmogorov parallel flow and homogeneous
isotropic turbulence. Furthermore, we examine the overall energy distribution
across the various scales of motion, highlighting the presence of small-scale
activity with a peak in the energy spectra occurring at the wavenumber
corresponding to the network spacing.
