Abstract
Birds in nature have many unique devices to help them acquire excellent flight abilities under various complex flight conditions. One of the unique devices is the leading-edge alula, located at the junction of the arm wing and the hand wing of most birds. It often spreads out during takeoff and landing, probably playing a similar role to high-lift devices in fixed-wing aircraft. This paper analyzed and reviewed the results of current research on leading-edge alula, finding some important factors, such as the complex flapping motions, flexibility, and the plane and section shape of the wing, that have been ignored in current research to a certain extent. These would greatly affect the conclusions obtained. Hence, for a deeper understanding of the aerodynamic mechanisms and functions of the alula, some new study predictions for future research are presented. In addition, the feasible models and methods for further research based on these predictions are discussed and proposed. For example, the higher-accuracy LES or hybrid LES/RANS method and the combinations of these methods with wind-tunnel experiments using PIV technology are recommended.
Highlights
Flying creatures in nature have evolved for millions of years, with excellent flight ability and environmental adaptability
We found that some critical factors were neglected to a ments and statistics
The results showed that the lift generated by the wing–leading-edge alula device (LEAD) assembly is very sensitive to the spanwise location of the LEAD, and the maximum lift improvement can be achieved when the LEAD is placed near the semispan length of the wing
Summary
Flying creatures in nature have evolved for millions of years, with excellent flight ability and environmental adaptability. With the increase in AoA, there is a risk of stalling, which is of great danger to flight At this time, birds often deflect their alula, playing a role similar to high-lift devices in fixed-wing aircraft [2]. The current research progress is analyzed, and comments on the current research are provided In clarifying this progress, we found that some critical factors were neglected to a certain extent, such as the complex flapping motions, flexibility, and the plane and section shape of the wing. On the basis of the study predictions, feasible research models and methods were discussed Through these analyses and discussions, on the one hand, the progress in current research on the alula can be clarified.
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