Tip vortex structure for a circular cylinder with a free end

The tip vortex structures near the free end of a circular cylinder of diameter D and height L were studied experimentally at a Reynolds number ReD=6×104. The cylinder was mounted normal to a ground plane and was partially immersed in a fully developed turbulent boundary layer. The cylinder aspect ratio was varied from AR=L/D=3 to 9, the boundary layer thickness-to-diameter ratio was δ/D=2.6, and the boundary layer thickness-to-height ratio ranged from δ/L=0.29 to 0.86. Wake surveys were conducted with a seven-hole pressure probe. The time-averaged velocity and streamwise vorticity fields showed the development of the tip vortices, the extent of the recirculation zone in the near-wake of the cylinder, and the downwash phenomenon. Additional streamwise vortex structures, known as base vortices, were identified within the boundary layer. These vortices were absent for the cylinder with AR=3, which had a distinctly different wake structure than the other cylinders.