In this study, we used the Taguchi method to derive the optimal design parameters for the grooves formed on the upper surface of a circular cylinder. Using the derived values of the optimal design parameters, we created grooves on diphycercal the surfaces of a circular cylinder and analyzed the wake flow and the boundary-layer flow of the circular cylinder. The streamwise time mean velocity and turbulence intensity of the wake flow field were used as the characteristics. Based on these characteristics, the optimal design parameter values were selected: n = 3, k = 1.0 mm (k/d = 2.5%), and θ = 60 deg. When the grooved cylinder was used, the streamwise time mean velocity in the wake of the cylinder showed 12.3% recovery, the wake width was reduced by 18.4% compared to the results from the smooth cylinder and we had 28.2% drag reduction from that of smooth cylinder. Also, the flow on the smooth cylinder separated at around 82 deg but the flow separation on a grooved cylinder appeared beyond 90 deg, that reducing the drag.
