| Summary: | Cylindrical structures subjected to flow are widely used in marine and offshore engineering and in structural applications. It has been shown that circular cylinder surface modifications can affect the separation point to move backward on the cylinder surface. Thus, reducing the drag coefficient. Flow past a circular cylinder with smooth, half and full rectangular, grooved surfaces (roughness coefficient k/D=0.04) were investigated in a low-speed open ended wind tunnel. The outer diameters (D) of the cylinders were 50mm and the depths (k) of the grooves were 2mm. The Reynold's number ranged from 1.65x104 to 1.13x105. The drag and lift coefficients of the cylinders were measured using a three-component balance. The wake flow patterns of the cylinders were observed using a smoke visualization technique. The results show that the full grooves and half grooves facing the flow produced a lower drag than a smooth cylinder with a half groove located at the leeside of the flow. The full grooved cylinder showed a drag reduction of 55% at Re=1x105. The presence of the groove on the cylinder's surface tripped the boundary layer and showed a smaller and narrower wake than a smooth cylinder.
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