Control of vortex shedding using a screen attached on the separation point of a circular cylinder and its effect on drag

The control of flow in the wake of a circular cylinder by an attached permeable plate having various porosity ratios was analyzed experimentally using both particle image velocimetry (PIV) and dye visualization techniques. The force measurements were also done in order to interpret the effect of control method on drag coefficient. The diameter of the cylinder and length to diameter ratio of the plate were kept constant as D=50mm and L/D=1.0, respectively. The porosity ratio, β, which can be defined as the ratio of open surface area to the whole body surface area, was taken as β=0.4, 0.5, 0.6, 0.7, and 0.8 (permeable plates). The study was performed considering deep water flow conditions with a constant Reynolds number of ReD=5000 based on the cylinder diameter. Each permeable plate was attached on the separation point and the results were compared with the results of cylinder without permeable plate (plain cylinder) in order to understand the control effect. Both qualitative and quantitative results revealed that the permeable plates of 0.4 ≤ β ≤ 0.6 are effective on controlling the unsteady flow structure downstream of the cylinder, i.e., the vortex formation length was increased, turbulent statistics was reduced and vortex shedding frequency was diminished when the permeable plate attached normal to the cylinder surface from the lower separation point. However, the drag force acting on the cylinder was found to be increased due to the increased cross-sectional area.