In this talk
we consider the onset of global instability in the flow past a row of
circular
cylinders placed in an oncoming uniform stream. A hybrid spectral method
is
used to first compute the steady flow and then investigate its linear
stability
by solving a generalised eigenvalue problem. Results have been obtained
for the
various mode classes, and our results show that for the odd-even modes
which
correspond to anti-phase oscillatory motion about the mid-plane between
the
cylinders, and are the ones most extensively studied in the literature,
the
effect of blockage has a marginal inuence on the critical Reynolds
numbers for
instability. This is in sharp contrast to results cited in many studies
with a
fully developed inlet flow past a cylinder placed between confining
walls. We
are also able to nd other unstable modes and in particular for low
blockage
ratios, the odd-odd modes which correspond to in-phase oscillatory
motion about
the mid-plane between the cylinders, are the first to become unstable as
compared
to the odd-even modes, and with much lower frequencies. |