  Turbulent flow evolution and energy cascades are significantly different in
two-dimensional (2D) and three-dimensional (3D) flows. Studies have
investigated these differences in obstacle-free turbulent flows, but solid
boundaries have an important impact on the cross-over between 3D to 2D
turbulence dynamics. In this work, we investigate the span effect on the
turbulence nature of flow past a circular cylinder at Re=10000. It is found
that even for highly anisotropic geometries, 3D small-scale structures detach
from the walls. Additionally, the natural large-scale rotation of the
K\'arm\'an vortices rapidly two-dimensionalises those structures if the span is
50% of the diameter or less. We show this is linked to the span being shorter
than the Mode B instability wavelength. The conflicting 3D small-scale
structures and 2D K\'arm\'an vortices result in 2D and 3D turbulence dynamics
which can coexist at certain locations of the wake depending on the domain
geometric anisotropy.
