Passive control of flow structures around a circular cylinder by using screen

The results of PIV measurements are presented in this paper for the water flow downstream of a circular cylinder surrounded with a screen (meshed outer control element) which had a streamlined shape. The diameter of cylinder, D was 50 mm and the Reynolds number based on the cylinder diameter was 5200. The characteristic length of the control element, L was tested for different cases so that the values of L/D were 2, 2.4, 2.8 and 3.2 in the experiments. It was noted that a forced reattachment of the shear layers separated from the cylinder was achieved by setting up the screen around the cylinder. As a consequence, the formation of vortical flow pattern was suppressed and turbulence statistics of the flow such as the intensity of turbulence, Reynolds shear stress, and turbulent kinetic energy were drastically diminished in comparison to the bare cylinder case. It was also found that the variable parameter of L/D did not dominantly influence the characteristics of the distribution of turbulence statistics along streamwise and transverse directions, however, the turbulence level decreased slightly for a smaller case of L/D.