  The flow of viscoelastic fluids in porous media is encountered in many
practical applications, such as in the enhanced oil recovery process or in the
groundwater remediation. Once the flow rate exceeds a critical value in such
flows, an elastic instability with fluctuating flow field is observed, which
ultimately transits to a more chaotic and turbulence-like flow structure as the
flow rate further increases. In a recent study, it has been experimentally
shown that this chaotic flow behaviour of viscoelastic fluids can be suppressed
by increasing the geometric disorder in a model porous media consisting of a
microchannel with several micropillars placed in it. However, the present
numerical study demonstrates that this is not always true. We show that it
depends on the initial arrangement of the micropillars for mimicking the porous
media. In particular, we find that for an initial ordered and aligned
configuration of the micropillars, the introduction of geometric order actually
increases the chaotic flow dynamics as opposed to that seen for an initial
ordered and staggered configuration of the micropillars. We suggest that this
chaotic flow behaviour actually depends on the number of the stagnation points
revealed to the flow field where maximum stretching of the viscoelastic
microstructure happens. Our findings and explanation are perfectly in line with
that observed and provided in a more recent experimental study.
