  The present work numerically investigates vortex-induced vibrations (VIV) of
a two-dimensional circular cylinder with an axisymmetric slit at Reynolds
number 500. The study examines the effects of slit shape (i.e., converging,
diverging, and parallel slits), the effect of slit-area ratios, slit-width, and
its angle with the freestream velocity on aerodynamic forces, vibration
response, and associated flow characteristics. The results demonstrate that the
addition of the slit assists the VIV suppression by adding an extra amount of
flow to the main flow. It results in the stabilized wake with the pressure
recovery downstream of the cylinder and causes a reduction in the lift force
over the cylinder. Also, there exist different shedding patterns associated
with different slit shapes. Proper Orthogonal Decomposition (POD) of the flow
field suggests that among all the three slits, the parallel slit heavily
modifies the flow behind the cylinder by distributing the amount of energy to a
large number of modes as compared to other slits (converging slit and diverging
slit), where the most of the energy is contained in a couple of modes. Further,
increasing the slit angle (for parallel slit) with respect to the freestream
increases the slit effectiveness up to a specific value of slit-angle and
beyond that starts to affect the VIV suppression adversely. Observations for
the effect of slit-width are also reported from the perspective of suppression
of VIV.
