Effect of leading-edge serration on the flow-structure interactions of an inverted flag

The effect of the leading-edge serrations on the dynamic behaviors and flow fields of an inverted flag is investigated using particle image velocimetry technique. Since the leading-edge serrations show a more obvious promotion effect on the flapping amplitude of an inverted flag in water tunnel than in wind tunnel, a detailed water tunnel experiment is further conducted. In the water tunnel experiment, like a clean inverted flag, the straight, periodic flapping, aperiodic flapping and deflected modes are also observed for a serrated inverted flag with a successive increase in flow velocity. The leading-edge serrations in water tunnel indeed significantly increase the flapping amplitude of a clean inverted flag without changing the critical flow velocities between the above four modes. This increase in amplitude is mainly attributed to the leading-edge serrations delaying the flow separation, which is also the high lift mechanism of a serrated flat plate. However, the leading-edge serrations with a wide width and a small vertex angle can change the shape of leading-edge vortex, thereby weakening the high lift effect. Therefore, in actual energy harvesting, it is a commendable choice to avoid selecting a serrated inverted flag with wide width and small vertex angle. Graphical Abstract: [Figure not available: see fulltext.]