Numerical investigations have been performed for the flow past square-section cylinders
with a spanwise geometric deformation leading to a stagnation face with a
sinusoidal waviness. The computations were performed using a spectral/hp element
solver over a range of Reynolds numbers from 10 to 150.Starting from fully developed shedding past a straight cylinder at a Reynolds
number of 100, a sufficiently high waviness is impulsively introduced resulting in
the stabilization of the near wake to a time-independent state. It is shown that
the spanwise waviness sets up a cross-flow within the growing boundary layer on
the leading-edge surface thereby generating streamwise and vertical components
of vorticity. These additional components of vorticity appear in regions close to the
inflection points of the wavy stagnation face where the spanwise vorticity is weakened.
This redistribution of vorticity leads to the breakdown of the unsteady and staggered
Kármán vortex wake into a steady and symmetric near-wake structure. The steady
nature of the near wake is associated with a reduction in total drag of about 16% at
a Reynolds number of 100 compared with the straight, non-wavy cylinder.Further increases in the amplitude of the waviness lead to the emergence of hairpin
vortices from the near-wake region. This wake topology has similarities to the wake
of a sphere at low Reynolds numbers. The physical structure of the wake due to
the variation of the amplitude of the waviness is identified with five distinct regimes.
Furthermore, the introduction of a waviness at a wavelength close to the mode A
wavelength and the primary wavelength of the straight square-section cylinder leads
to the suppression of the Kármán street at a minimal waviness amplitude.
Effect of Reynolds numbers on flow past four square cylinders in an in-line square configuration for different gap spacings
