  Flexible canopy flows are often encountered in natural scenarios, e.g., when
crops sway in the wind or when submerged kelp forests are agitated by marine
currents. Here, we provide a detailed characterisation of the turbulent flow
developed above and between the flexible filaments of a fully submerged dense
canopy and we describe their dynamical response to the turbulent forcing. We
investigate a wide range of flexibilities, encompassing the case in which the
filaments are completely rigid and standing upright as well as that where they
are fully compliant to the flow and deflected in the streamwise direction. We
are thus able to isolate the effect of the canopy flexibility on the drag and
on the inner-outer flow interactions, as well as the two flapping regimes of
the filaments already identified for a single fiber. Furthermore, we offer a
detailed description of the Reynolds stresses throughout the wall-normal
direction resorting to the Lumley triangle formalism, and we show the
multi-layer nature of turbulence inside and above the canopy. The relevance of
our investigation is thus twofold: the fundamental physical understanding
developed here paves the way towards the investigation of more complex and
realistic scenarios, while we also provide a thorough characterisation of the
turbulent state that can prove useful in the development of accurate turbulence
models for RANS and LES.
