Effects of Leading-Edge Protuberances on Airfoil Performance

TLDR

The study examines leading‑edge sinusoidal protuberances whose size and spacing match those seen on humpback whale flippers. Lift, drag, and pitching moments of the modified airfoils were measured in a water tunnel, with protuberance amplitudes of 2.5–12 % of chord and wavelengths of 25–50 % of chord, and flow visualization using tufts examined separation. Below the baseline stall angle the modified foils exhibit reduced lift and increased drag, whereas above stall they achieve up to 50 % higher lift with minimal drag penalty, with amplitude driving performance changes and flow visualization showing trough‑originated separation and peak‑attached flow.

Abstract

Lift, drag, and pitching moments of airfoils with leading-edge sinusoidal protuberances were measured in a water tunnel and compared with those of a baseline 63 4 -021 airfoil. The amplitude of the leading-edge protuberances ranged from 2.5 to 12% of the mean chord length; the spanwise wavelengths were 25 and 50% of the mean chord length. These ranges correspond to the morphology found on the leading edge of humpback whales' flippers. Flow visualization using tufts was also performed to examine the separation characteristics of the airfoils. For angles of attack less than the baseline stall angle, lift reduction and drag increase were observed for the modified foils. Above this angle, lift of the modified foils was up to 50% greater than the baseline foil with little or no drag penalty. The amplitude of the protuberances had a distinct effect on the performance of the airfoils, whereas the wavelength had little. Flow visualization indicated separated flow originating primarily from the troughs and attached flow on the peaks of the protuberances at angles beyond the stall angle of the baseline foil.