Effect of local waviness in confining walls and its amplitude on vortex shedding control of the flow past a circular cylinder

Numerical investigation of vortex shedding control and its suppression due to flow past a circular cylinder has been carried out starting from the Reynolds number 20 and upto the appearance of first instability in the wake. A technique “local waviness” is used in the confining walls for the effective control of shedding. The local waviness with crest near the cylinder wake eliminates vortex shedding with reduced drag (Deepakkumar et al., 2017). Effect of amplitude of local waviness on vortex shedding characteristics are systematically carried out and presented in this article. It is found that local waviness with amplitude A = 0.15D is an optimum value for effective vortex shedding suppression with reduced drag on the cylinder at Re = 200. As the amplitude of waviness increases, the wake size is reduced significantly as compared with plain wall confined cylinder. The presence of crest closer to the cylinder in the downstream generates a favorable pressure gradient and prevents flow separation at Reynolds number 20. The pressure drag is controlled significantly by the trough region in the waviness, whereas the crest region affects both pressure and frictional drag. Also, the appearance of first instability in the flow is identified for different amplitude of waviness.