  In this paper, we report new insight into a symmetry-breaking phenomenon that
occurs for turbulent flow in periodic porous media composed of cylindrical
solid obstacles with circular cross-section. We have used Large Eddy Simulation
to investigate the symmetry-breaking phenomenon by varying the porosity
(0.57-0.99) and the pore scale Reynolds number (37-1,000). Asymmetrical flow
distribution is observed in the intermediate porosity flow regime for values of
porosities between 0.8 and 0.9, which is characterized by the formation of
alternating low and high velocity flow channels above and below the solid
obstacles. These channels are parallel to the direction of the flow.
Correspondingly, the microscale vortices formed behind the solid obstacles
exhibit a bias in the shedding direction. The transition from symmetric to
asymmetric flow occurs in between the Reynolds numbers of 37 (laminar) and 100
(turbulent). A Hopf bifurcation resulting in unsteady oscillatory laminar flow
marks the origin of a secondary flow instability arising from the interaction
of the shear layers around the solid obstacle. When turbulence emerges,
stochastic phase difference in the vortex wake oscillations caused by the
secondary flow instability results in flow symmetry breaking. We note that
symmetry breaking does not occur for cylindrical solid obstacles with square
cross-section due to the presence of sharp vertices in the solid obstacle
surface. At the macroscale level, symmetry-breaking results in residual
transverse drag force components acting on the solid obstacle surfaces.
Symmetry-breaking promotes attached flow on the solid obstacle surface, which
is potentially beneficial for improving transport properties at the solid
obstacle surface such as convection heat flux.
