PIV Flow Field Measurements of Hovering Rotors with Leading-Edge Protuberances

Performance and phase-resolved particle image velocimetry (PIV) measurements were taken on a rotor hovering out of ground effect to examine the wake structure generated by blades with leading-edge protuberances. The effects of protuberance amplitude and wavelength were examined using four sets of blades with various sinusoidal leading edges, as well as a baseline rectangular blade. At lower thrust conditions, the baseline and modified blades had similar power requirements. However, as thrust increased, the modified blades required additional power compared to the baseline. Specifically, the additional power requirements were found to be directly related to protuberance amplitude, whereas wavelength had a minimal effect. PIV measurements were taken with the rotor operating at a blade loading coefficient of 0.12. The baseline and low amplitude blades produced similar flow fields, containing a concentrated tip vortex that persisted to late wake ages and a less intense wake sheet. Conversely, the higher amplitude blades produced significantly more intense wake sheets and less coherent tip vortices, which persisted for less than one rotor revolution. Furthermore, the higher amplitude blades also generated a more uniform spanwise inflow distribution.