The Investigation of the effect of the helical strakes'height on the cylindrical wake

In this study, the wake behind a cylinder with helical strakes at Re = 20000 is experimentally investigated. Three helical strakes with a pitch of 3D and equal distances were installed on the cylinder. The ratios of strakes heights (thicknesses) to cylinder diameter (H/D) were 0.1, 0.09, 0.07 and 0.05. The effects of helical strakes on the mean velocity profile, turbulence intensity, velocity defect and Strouhal number of the cylinder on its center line were studied. The results showed that using helical strakes with varying heights results in different effects on the wake structure, which can be demonstrated in near (x≤D) and far (x>D) regions downstream, behind the model. In the near regions, planes with higher thickness resulted in improved wake and reduced velocity defect, while in the far regions, using the plane with an H/D of 0.07 led to up to 35% decrease in velocity deficit. Rotating planes helical strakes were also seen to reduce maximum turbulence by 14%.