Experimental Investigation of Bio-Inspired Geometries for Modulating the Horseshoe Vortex Around a Cylinder

Abstract

This study experimentally investigates the influence of bio-inspired surface morphologies on the near-wall flow developing upstream of wall-mounted cylindrical piers. Planar two-dimensional two-component Particle Image Velocimetry measurements are performed in a closed-loop water tunnel facility at the University of Tuscia. The analysis focuses on the vertical measurement plane upstream of the pier and on the near-wall region, where the interaction between the incoming boundary layer and the cylinder controls flow separation and upstream recirculation. A smooth circular cylinder is used as the baseline configuration and compared with ridged bio-inspired models. The results show that the smooth cylinder produces a pronounced near-wall reverse-flow region together with a wall-normal motion directed toward the bed. These features represent characteristic planar signatures of the separated flow associated with the horseshoe vortex system. The introduction of surface ridges substantially modifies these signatures. Compared with the smooth cylinder, the ridged configurations reduce the extent of the reverse-flow region observed in the measurement plane and weaken or spatially redistribute the downward wall-normal velocity component.