  The present article aims to study the suppression of vortex shedding using a
passive flow control technique (slit through a circular cylinder) in the
laminar regime (Re=100-500). The slit width ratio S/D (slit width/diameter) on
the modified cylinder plays an essential role to control the vortex shedding.
The additional flow through the slit leads to the suppression of the global
instability and vortex shedding, whereas a large amount of flow through the
slit drastically alters the behavior of vortex shedding. The nature of vortex
shedding remains periodic for all S/D, and the root mean square (rms) value of
the lift coefficient decreases (in turn, vortex shedding suppression) with S/D
up to Re = 300. For the range Re > 300, the root mean square (rms) value of the
lift coefficient decreases up to S/D < 0.15, and the flow exhibits periodic
vortex shedding, while the root mean square (rms) increases beyond S/D > 0.15
due to irregular vortex shedding downstream of cylinder. The variation of the
Re for the S/D=0.20 shows bifurcation points where the flow changes its
behavior from symmetric to asymmetric solution at Re=232 and again becomes
symmetric at Re=304. The unsteady flow analysis over the modified cylinder also
indicates the suppression in the vortex shedding; however, the analysis
provides the qualitative property of suppression. The reduced order modeling,
i.e. Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition
(DMD), is utilized to quantify suppression and investigate the dominant
vortical structure for slit through the cylinder.
