Passive flow control downstream a circular cylinder using perforated circular cylinder in deep water

The aim of the present study was to control the vortex shedding downstream of a circular cylinder (inner cylinder) by the existence of outer perforated cylinder concentrically located around the inner cylinder in deep water. The flow characteristics downstream of concentrically placed coupled (shrouded) cylinders were investigated quantitatively by the Particle Image Velocimetry (PIV) technique. Diameter of the outer perforated cylinder was kept constant as Do=100 mm while diameter of the inner cylinder was varied within the range of 25? Di ?90 mm. The depth-averaged free-stream velocity was also kept constant as U=100 mm/s which corresponded to the Reynolds number of ReDo=10,000 based on the outer cylinder diameter. Experiments were conducted for seven porosities (ß=0.25, 0.30, 0.40, 0.50, 0.60, 0.70 and 0.80) and nine diameter ratios (Di/Do=0.25, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80 and 0.90) in order to show the effect of these parameters on the flow control. Maximum values of both Reynolds shear stress and turbulence kinetic energy significantly decreased with the existence of outer perforated cylinder and also, the location of peak magnitudes of turbulence statistics occurred at locations further downstream compared to the bare cylinder cases. The most effective control was revealed for the porosity range of 0.50?ß?0.60 for all diameter ratios. It was concluded that the perforated cylinder could be used as a passive control element as indicated by the results presented in this study. Key Words: Cylinder, Passive control, PIV, Turbulence Kinetic Energy, Deep water