Flows dictate the incipient fluctuating loading and are influenced

Flows past cylindrical geometries are encountered in numerous engineering applications, e.g.,civil structures, heat exchangers, pipelines, antennae and various energy harvesting systems. Cylindrical structures immersed in a flow produce wake vortex shedding which may trigger the mechanism of flow-induced vibrations, leading to structural fatigue and earlier failure. When the Reynolds number is sufficiently large ({Re extsubscript{D}}$>$50), vortex shedding occurs in the wakes of such structures. The periodic shedding of vortices induces fluctuating forces on the cylinder and may lead to Vortex Induced Vibrations (VIVs).paragraph{}Over the past several decades, various methods for passive suppression of vortex shedding aimed at mitigating VIV have been considered, including alterations to cylinder geometry with helical strakes, fins, sleeves, and fairings.By reducing the spanwise coherence of vortices, these methods primarily reduce the magnitude of the fluctuating lift and drag forces on cylindrical structures. Similar alterations to cylinder geometry have been shown to also significantly reduce mean drag on cylindrical bodies, e.g., cylinders with wavy sinusoidal front faces,cylinders with hemi-spherical surface bumps,cylinders with a sinusoidally varying diameter or cylinders with multiple step discontinuities in diameter.paragraph{}For structures with a uniform circular cross section, wake vortex shedding is often described in terms of the characteristic frequency, the size and position of vortex formation region, the strength of vortices at formation, and the spanwise correlation length. These parameters largely dictate the incipient fluctuating loading and are influenced significantly by the Reynolds number ({Re extsubscript{D}), the incoming flow uniformity and turbulence intensity,the aspect ratio of the cylinder, and the cylinder end conditions. Often these parameters cannot be modified in practice, and either passive or active flow control strategies are sought to reduce the unsteady and/or mean loading on the structure. For example, such passive geometrical modifications to cylinder geometry as the addition of splitter plates, roughness elements, helical strakes, step changes in cylinder diameter can be used to effectively alter the spanwise coherence and strength of vortex shedding and even suppress vortex shedding.