SINOPSIS

Flow around circular cylinders with different groove surfaces (U and V-shaped) was investigated experimentally. The results were compared with those from a smooth cylinder of the same diameter D. The drag force, mean velocity and turbulence intensity profiles of the wake behind the cylinders were measured for Reynolds numbers in the range Re_D = 8×10³ ~ 1.4×10⁵. At Re_D = 1.4×10⁵, the U-type groove surface reduced the drag coefficient by 18.6% compared with the smooth cylinder, whereas the drag reduction of V-type groove was only 2.5%. The two riblet surfaces tested in this study display different surface pressure distributions at high Reynolds numbers due to their different flow structures near the cylinder surface. Flow around the cylinders was visualized using a particle tracer technique to qualitatively investigate the flow structure. The longitudinal secondary vortices formed behind the grooved cylinders are more active and show rapid flow motion, compared with the smooth cylinder.