An experimental study on flow separation control of hydrofoils with leading-edge tubercles at low Reynolds number

Hydrodynamic characteristics of hydrofoils with leading-edge tubercles were experimentally investigated in a water tunnel at a Reynolds number of Re=1.4 x 10(4). Particle image velocimetry measurements and particle-streak visualizations reveal that the tubercles improve flow separation behaviour. In particular, hydrofoils with larger wave amplitudes and smaller wavelengths tend to perform significantly better in flow separation control. Cross-stream flow measurements indicate that streamwise counter-rotating vortex pairs are generated over the tubercles and mitigate flow separation. Analysis confirms. that the tubercles function as vortex generators, due to their comparable heights relative to the boundary layer thickness. The vortex pairs meander and interact with adjacent flows, causing the flow separation behaviour to be occasionally unstable, thus leading to variable flow separation region sizes. This suggests that measures may have to be taken to ensure the stability of the counter-rotating vortex pairs for more persistent and predictable improvements. (C) 2015 Elsevier Ltd. All rights reserved.