Vortex street suppression of a circular cylinder using perforated semi-circular fairing in shallow water

In this study, the effect of perforated fairing on vortex street suppression of a circular cylinder was investigated experimentally in shallow water. In order to investigate the effect of arc angle, α and porosity, β which are the main parameters of the study, three different arc angles (α = 120°, 150° and 180°) and six different porosities (β = 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were examined. Perforated fairing was concentrically located with respect to the circular cylinder along its downstream direction. Turbulent statistics (turbulent kinetic energy, TKE and Reynolds shear stress, 〈u′v′〉) in the wake region were obtained by employing particle image velocimetry (PIV) technique at a Reynolds number of ReD = 5 × 103 based on the circular cylinder diameter, D. The results depicted that the flow structure downstream of bare cylinder was significantly affected by the presence of perforated fairing for the porosity, β values, in the range of β = 0.3-0.6. It is found that the wake region of the cylinder was elongated substantially along the main flow direction and the vortex shedding frequency, was reduced substantially. Moreover, opposing shear layers lost their strength considerably compared with the bare cylinder case. The peak magnitude of Reynolds shear stress, 〈u′v′〉 was reduced up to 75% for the arc angle of α = 180° and the location of peak magnitude of Reynolds shear stress, 〈u′v′〉 moved further downstream regions for all cases. Compared to the bare cylinder case, the most effective flow control was obtained for the case having β = 0.6 porosity and α = 180° arc angle.