Flow control downstream of a circular cylinder by a permeable circular cylinder in deep water

The aim of this study is to investigate the flow structure downstream of a circular cylinder surrounded by an outer permeable cylinder which is made from chrome-nickel wire mesh in deep water using Particle Image Velocimetry technique. All experiments were performed at Reynolds number 5000 based on the inner cylinder diameter. In order to understand the effects of diameter and porosity of the outer cylinder on the flow structures of the inner cylinder, seven different outer cylinder diameters (D=37.5, 45, 52.5, 60, 67.5, 75 and 90 mm) and eight different porosities (ß=0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85) were considered. During the experiments, the diameter of inner cylinder was kept constant as d=30 mm. The experimental results indicated that both the diameter ratio and the porosity are important parameters to control the flow structure behind the inner cylinder-outer permeable cylinder arrangement. The outer permeable cylinder significantly suppressed the vortex shedding downstream of the inner cylinder-outer permeable cylinder arrangement for the diameter ratio greater than D/d=1.5. The effect of D/d= 3.0 on the attenuation of vortex shedding downstream of the inner cylinder-outer permeable cylinder arrangement was much more pronounced compared to other diameter ratios. Furthermore, the effectiveness of the outer permeable cylinder increased as the value of porosity increased up to ß=0.7. In terms of the case of the permeable cylinder without the inner cylinder, the flow structure downstream of the permeable cylinder was independent of the diameter of the permeable cylinder