Flow control downstream of a circular cylinder by perforated semi circular cylinder in shallow water

In this study, it was aimed to control the unsteady flow occurred in the near wake of a circular cylinder in shallow water. Outer cylinders of six different porosities (ß=0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) and three different arc angles (?=120o, 150o and 180o) were used as control equipment. Nine different cylinder diameters (Di=25mm, 30mm, 40mm, 50mm, 60mm, 70mm, 75mm, 80mm and 90mm) were used in order to examine the effect of the diameter ratio. The depth-averaged free-stream velocity was also kept constant as U=100 mm/s which corresponded to a Reynolds number of ReDo=10,000 based on the outer cylinder diameter. The data obtained from the experiments showed that the arc angle of perforated cylinders affect flow control significantly and that the optimum arc angle was ?=180o. It was observed that although the outer cylinders with ?=120o and ?=150o arc angle were effective on smaller diameter ratios, they lost their effectiveness on the flow structure at higher diameter ratios. The time averaged vorticity contours and Turbulence Kinetic Energy statistics show that porosity is highly effective on the flow structure. It was concluded for ?=180o outer cylinder arc angle that the ideal porosities in moving away the unsteady flow in the near wake of cylinder and reducing the peak magnitude of Reynolds stress were ß=0.5 and 0.6. It was determined that the most effective diameter ratio with which unsteady vorticity move the point where Turbulence Kinetic Energy contours occur further downstream was Di/Do=0.5. Di/Do=0.75 was determined the most ideal diameter ratio in reducing Turbulence Kinetic energy value and the peak magnitude of Reynolds stress compare with bare cylinder case.