FISH, Frank E.; MIKLOSOVIC, David S.; MURRAY, Mark M.; HOWLE, Laurens E.; West Chester University; U.S. Naval Academy; U.S. Naval Academy; Duke University: Delayed stall due to leading edge tubercles of the humpback whale flipper
The humpback whale (Megaptera novaeangliae) is exceptional among the baleen whales in its ability to undertake acrobatic underwater maneuvers. In order to bank and turn, humpback whales use mobile, wing-like flippers. The humpback whale flipper is unique because of the presence of large tubercles on the leading edge, giving this surface a scalloped appearance. The position, size and number of tubercles suggest analogues with specialized leading edge control devices for improvements in hydrodynamic performance on lifting surfaces. It was hypothesized that these leading edge tubercles can modify the hydrodynamic characteristics of the flipper to enhance turning. Precision wind tunnel measurements were performed on 1/4 scale models of an idealized humpback whale flipper with and without the simulated tubercles. The model with the tubercles along its leading edge was shown to maintain lift and delay stall to angles of attack approximately 40% higher than a flipper without the tubercles. The tapered design of the flipper indicates that flow separates on the distal region, resulting in tip stall, but with only a partial loss of lift. Drag on the flipper with tubercles was lower than the smooth flipper over the range of angles of attack of 12o to 17.5o. Lift-to-drag ratio of the flipper with tubercles was maximal at a value of 22.3 for an angle of attack of 7.5o. Tubercles function to produce vortical flows of water moving over the surface of the flipper and control lift characteristics at high angles of attack, where stall would occur. The ability to maintain lift at high angles of attack would be advantageous for the humpback whale during tight turns associated with the whale’s foraging behavior.
