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PIV Flow Field Measurements of Hovering Rotors with Leading Edge Protuberances
NAVAL ACADEMY ANNAPOLIS MD ANNAPOLIS United States
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The ability of a helicopter to hover and takeoffland vertically makes it uniquely suited for many different missions. However, its relatively low forward flight speed has led to a focus on developing helicopters with significantly higher velocity ceilings. The inspiration for the use of protuberances stems from the leading-edge of the pectoral flipper on the humpback whale which, despite its large size, has exceptional maneuverability i.e., small turning radius among other whale species. This project utilized thrust and torque measurements and high-resolution particle image velocimetry PIV measurements to analyze performance and wake characteristics of rotors with leading-edge protuberances. Four modified blades, with sinusoidal leading-edges of various amplitudes and wavelengths, were compared to a fifth baseline design. As thrust increased, the modified blades required additional power compared to the baseline this power increase was directly related to protuberance amplitude, while wavelength had a minimal effect. The baseline and low amplitude blades produced similar flow fields a concentrated tip vortex and a less turbulent wake sheet. Conversely, the higher amplitude blades produced a significantly more turbulent wake sheet and less coherent tip vortices that dissipated quickly. The higher amplitude blades created more uniform and more ideal inflow across the rotor disk, but the generation of vortices along these blades most likely contributed to their greater power requirements.
APPROVED FOR PUBLIC RELEASE