On the disruption of the horseshoe vortex in flow past bed-mounted cylinders

The present study investigates the disruption of the horseshoe vortex (HSV) formed around a bed-mounted circular cylinder using helical strakes. Three cylinders were studied: one plain and two with helical strakes, oriented at 30° and 0° to the vertical mid-plane, respectively. A planar particle image velocimetry technique was employed for the measurement of the velocity field near the upstream cylinder-bed junction. The results revealed that strakes oriented at 0° prevent the formation of the HSV by disrupting the downward flow near the cylinder-bed junction. In contrast, a strong downflow was observed near the bed for the plain and 30° straked cylinder. The 0° helical strakes can be potentially used as scour-countermeasure around the pier due to their ability to disrupt the HSV. Analysis of turbulent stresses further demonstrated that the 0° straked cylinder experienced a reduction in Reynolds shear stress compared to both the plain and 30° straked cylinder.