The Effect of Humpback Whale-like Protuberances on Hydrofoil Performance Public
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Despite its size the humpback whale is extremely maneuverable. This has been attributed to their use of pectoral flippers, along which protuberances are present along the leading edge. There has been speculation that the protuberances along the leading edge of the pectoral flipper act as a form of passive flow control. To examine the effects of protuberances on hydrofoil performance, the lift, drag, and pitching moments of two-dimensional hydrofoils with leading edge sinusoidal protuberances were measured in a water tunnel and compared to those of a baseline NACA 634-021 hydrofoil. The amplitude of the protuberances ranged from 2.5% to 12% of the mean chord length and the spanwise wavelengths were 25% and 50% of the mean chord length. This corresponds to the morphology found on the leading edge of humpback whaleâ€™s flippers. Flow visualization using tufts and dye was also performed to examine the near surface flow patterns surrounding the hydrofoils. At angles of attack lower than the stall angle of the baseline the modified foils revealed reduced lift and increased drag. However, above this angle the lift generated by the modified foils was up to 50% greater than the baseline foil with little or no drag penalty. The amplitude of the protuberances has a large effect on the performance of the hydrofoils whereas the wavelength has little. Corroborating lift and drag measurements, visualizations show attached flow on the peaks of the protuberances and separation in the valleys at angles beyond the stall angle of the baseline foil.
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