Flow control of a cylinder in shallow water using perforated cylinder

The aim of this experimental study was to control the vortical flow structure downstream of a circular cylinder (inner cylinder) as well as the surrounding outer perforated cylinder in shallow water flow. Experiments were performed using both special dye visualization and a laser-based particle image velocimetry technique. Experiments consisted of two parts; i) Vortex shedding behavior around a perforated cylinder was investigated with the porosity, ß in the range of 0.1?ß?0.8 for the Reynolds number of ReDo=10,000 and outer perforated cylinder diameter of Do=100mm and ii) The effects of porosity, ß and the inner cylinder diameter to the outer perforated cylinder diameter ratio, Di/Do on the unsteady flow characteristics around both inner and outer perforated cylinders were analyzed. Experiments were conducted for nine different diameter ratios within the range of 0.25?Di/Do?0.8, 15 different porosity, ß and three different Froude numbers, (Fr=0.2, 0.3 and 0.4). PIV measurements showed that the porosity, ß and diameter ratio, Di/Do have a substantial effect on the suppression of vortex shedding and the consequent Karman Vortex Street. The velocity fluctuations in the wake region of inner cylinders were substantially affected by the existence of outer perforated cylinder which is concentrically located around the inner cylinder. The values of the optimum porosity, ß to control the unsteady flow structure were found to be ß=0.75, 0.6, 0.55 and 0.4 for the diameter ratios of Di/Do=0.25, 0.5, 075, and 0.9, respectively.