The aim of this study is the control of unsteady vortical flow occurred downstream of a circular cylinder located in shallow water flow using concentrically located outer perforated cylinder. The porosities, ȕ have been changed between 0.1 and 0.8 in the present study. The increments of porosity ȕ were taken as 0.05 in the range of 0.1 and 0.8 with a hole diameter of d=10 mm. The ratio of inner cylinder diameter to outer cylinder diameter, D i /D o was selected as 0.25, 0.3, 0.4, 0.5 and 0.6

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... inner cylinder diameter is D i =50mm where the outer cylinder diameter is D d =100mm. Experiments were performed at a constant depth of the water level as h=50mm (half of the outer cylinder diameter). Free stream velocity was taken as U =100 mm/s corresponding to a Reynolds number of Re D o =10000 based on the outer cylinder diameter. It has been observed that the inner circular cylinder was highly affected by the existence of surrounding outer perforated cylinders. It is observed that the intensity of Reynolds shear stress correlating, is completely attenuated in the region both downstream of concentric cylinder and between the concentric cylinders. It is determined from the experiments that porosity, ȕ=0.55 is the most effective parameter for control of flow structure that is occurred from the inner cylinder.