STALL MECHANISM ANALYSIS OF HUMPBACK WHALE FLIPPER MODELS

摘要

Previous research has shown that large rounded tubercles on the leading edge of humpback whale flipper models can delay stall angle by up to 40% while improving the drag performance over a range of attack angles (Miklosovic, 2004) The tubercles suggest a correlation to other control devices such as vortex generators and wing fences. The research that highlighted the superior stall behavior of tubercled leading edge flippers compared to smooth leading edge flippers was carried out using half span wing models of whale flippers. The stall behavior of wing models can be complicated by the progression of stall over the span of the wing. The research described in this paper involves the construction, testing and analysis of several airfoil models in order to better understand the stall mechanism(s) associated with the humpback whale flipper. Since airfoils have no root or tip, stall ideally occurs over the entire span. Three different airfoil models, one with leading edge tubercles, one with a smooth leading edge and the third with a smooth leading edge and vortex generators, were tested in an open circuit wind tunnel at the U.S. Naval Academy. By comparing the stall behavior of airfoils with smooth and tubercled leading edges, the function of the tubercles as a spanwise or chordwise stall inhibitors was explored. A smooth airfoil with conventional vortex generators was also tested for comparison with the tubercled airfoil. The results obtained indicate that the tubercled airfoil produces less lift and more drag than a smooth airfoil through a range of attack angles. The inferior performance of the tubercled airfoil suggests that the function of the tubercles on half span humpback whale fins tested by Miklosovic et al. (2004) may be tied to the spanwise progression of stall.