Alula bird5/15/2023 ![]() First, that the alula generates a small vortex which separates the attached-flow system on the inner, thick-profiled, arm-wing section and the separated leading-edge vortex (LEV) on the outer, thin-profiled, hand-wing section. These observations have prompted a revaluation of the aerodynamics of the alula for which two updated interpretations of its function have been proposed 4, 6. Subsequent research depicting separated flow over real and model swift wings in steady flight 15, 16 and Passerines in slow-flapping flight 17 suggests that the alula likely prevents wing stall through the maintenance of separated-edge flows rather than preventing flow separation from occurring in the first place. These devices prevent wing stall by ensuring the flow remains smoothly attached to the wing. 1) has led to early comparisons of it to flow control devices on aircraft such as leading-edge slots/slats 7, 8, 9. The gap formed between the deflected alula and the top surface of the wing (see Fig. These findings shed new light on avian wing anatomy and the role of unconventional aerodynamics in shaping it.įull size image Aerodynamics of the alulaĭespite consensus among researchers regarding the importance of the alula in avian flight, the aerodynamic mechanisms underlying its function remain debated. We found the position of the alula on non-aquatic birds selected for alula optimization to be located at or near the lift-maximizing position predicted by wind tunnel experiments. To test this, we perform experiments on model wings in a wind tunnel to approximate this distance and compare our results to positional measurements of the alula on spread-wing specimens. Specifically, we test the hypothesis that the relative distance of the alula from the wing tip is that which maximizes LEV-lift when the wing is spread and operated in a deep-stall flight condition. Here, we explore scaling trends of the alula’s spanwise position and its connection to this function. New research into the aerodynamics of this structure suggests that its primary function is to induce leading-edge vortex (LEV) flow over bird’s outer hand-wing to enhance wing lift when manuevering at slow speeds. The authors aim to apply the way that the alula works in designing a device that enables the air vehicles to turn better and more efficiently.An aerodynamic structure ubiquitous in Aves is the alula a small collection of feathers muscularized near the wrist joint. Haecheon Choi, the corresponding author of the paper. The role of the alula in avian flight is just one example." says Dr. "Nature is full of vortices, and the animals and plants use them wisely. But this is the first time that the researchers found the evidence that the effect of the alula is due to a small vortex formed at the tip of the alula feathers. There have been several other attempts to reveal the role of the alula in birds' flight. Measurements of the forces acting on wings in the wind tunnel proved that indeed the presence of the vortex from the alula helps the birds in flight. Although the alula is small, it creates enough vortex to prevent the air flow from being detached from the wing." says Dr. "For the wing to fly better, the air has to move closer to the wing. Here they observed that a tiny vortex from the alula tip presses the air flow over the wing and makes the air flow better attached to the wing surface. Then the researchers moved on to the wind tunnel experiments where they visualized the movement of tiny particles around magpie wings. "But with the alula they seem to turn more easily." ![]() Sang-im Lee, the first author of the paper. "It's not that they cannot fly without the alula." says Dr. ![]() They started with observing magpies in the aviary when the birds moulted the alula feathers. The researchers were interested in the flight of magpies. This study was conducted by a research team of biologists and mechanical engineers at the Seoul National University. A recent article published in Scientific Reports says that the secret is a small vortex of air that is formed at the tip of the alula feathers. ![]()
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