Abstract
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, β have been changed between 0.1 and 0.8 in the present study. The increments of porosity β 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, Di /Do was selected as 0.25, 0.3, 0.4, 0.5 and 0.6 the inner cylinder diameter is Di =50mm where the outer cylinder diameter is Dd =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 Do =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, β=0.55 is the most effective parameter for control of flow structure that is occurred from the inner cylinder.
Highlights
A bluff body such as a cylinder which is placed in a flow alters the general characteristics of the flow structure
In order to reduce or eliminate the adverse effects of vortex-induced vibrations (VIV), it is inevitably important to control the flow structure around the bluff body and/or alter the mechanical properties of the material used in terms of damping and natural frequency
Kelvin-Helmholtz vortices appear along the shear layer of the concentric cylinders. It can be seen clearly from dye experiments that diameter ratio is an important parameter on the control of Karman vortices formed by the inner cylinder or outer perforated cylinder. It is determined from the dye experiments that porosity, ȕ and diameter ratio of inner and outer cylinders, Di/Do are the two significant parameters on the control of flow structure generated by the inner cylinder
Summary
A bluff body such as a cylinder which is placed in a flow alters the general characteristics of the flow structure. This alteration causes more complex and unsteady flow characteristics like resonance and highamplitude of fluctuating forces and have important implications for flow-induced vibration and noise generation. In order to reduce or eliminate the adverse effects of vortex-induced vibrations (VIV), it is inevitably important to control the flow structure around the bluff body and/or alter the mechanical properties of the material used in terms of damping and natural frequency. Every et al [10] stated in their review that the flow can be controlled by means of an alteration of the structural profile in order to affect the separation of the boundary layer to prevent the occurrence of vortex shedding along the length of the structure or alter the formation of the wake vortices and their interactions
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