In the present study, flow control mechanism of single groove on a circular cylinder surface is presented experimentally using Particle image velocimetry (PIV). A square shaped groove is patterned longitudinally on the surface of the cylinder with a diameter of 50 mm. The flow characteristics are studied as a function of angular position of the groove from the forward stagnation point of the cylinder within 0 degrees <= theta <= 150 degrees. In the current work, instantaneous and time-averaged flow data such as vorticity, omega streamline, Psi streamwise, u/U-o and transverse, v/U-o velocity components, turbulent kinetic energy, TKE and RMS of streamwise, u(rms) and transverse, v(rms) velocity components are utilized in order to present the results of quantitative analyses. Furthermore, Strouhal numbers are calculated using Karman vortex shedding frequency, f(k) obtained from single point spectral analysis. It is concluded that a critical angular position of the groove, theta = 80 degrees is observed. The flow separation is controlled within 0 degrees <= theta <= 80 degrees. At theta = 80 degrees, the flow separation starts to occur in the upstream direction. The instability within the shear layer is also induced on grooved side of the cylinder with frequencies different than Karman vortex shedding frequency, f(k). (C) 2017 Elsevier Inc. All rights reserved.