Exploring Near-Wake Structures: Bio-Inspired Convergent-Divergent Riblets on Circular Bluff Bodies

Convergent-divergent (C-D) riblets represent a pioneering rough surface inspired by the skin of fast-swimming sharks and flight feathers of the birds. In this study, we applied convergent-divergent riblets to the outer surface of a circular cylinder to examine their influence on the near-wake flow structure behind the cylinder. Various experimental techniques, such as particle image velocimetry (PIV), hot-wire anemometer, and a load cell for force measurement, were employed for this study. The experimental measurements have been conducted at different Reynolds numbers ranging from (6–12) ×103. The findings from force measurement indicate a decrease in the mean drag coefficient of around 14%, 15%, 11%, and 12% obtained by riblets at Re = 6000, 7500, 10,000, and 12,000, respectively. The time-averaged flow field including streamlines, velocity field, Reynolds shear stress, vorticity, and turbulent kinetic energy were measured. The measurements suggest that the wake's size has decreased by using convergent-divergent riblets. Furthermore, data obtained from the hot-wire anemometer reveal that these riblets alter the vortex shedding frequency to a higher value and impact the amplitude peak of the power spectrum at various Re numbers.