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The function of the alula in avian flight
Sang-im Lee1, Jooha Kim2, Hyungmin Park3
11] Institute of Advanced Machines and Design, Seoul National University, Seoul, Korea [2] School of Biological Sciences, Seoul National University, Seoul, Korea.
Scientific Reports
|May 8, 2015
Summary
The alula, a bird
Area of Science:
- Avian biomechanics
- Aerodynamics
- Animal flight
Background:
- The alula is a small avian feather structure.
- Its function in flight, particularly in delaying stall, is widely accepted but poorly understood.
- Assumed to act like a leading-edge slat to increase lift.
Purpose of the Study:
- To investigate the aerodynamic function of the alula in avian wings.
- To elucidate the mechanism by which the alula delays stall and aids flight.
Main Methods:
- Flight tasks and wind-tunnel experiments.
- Force measurements.
- Digital particle image velocimetry (DPIV).
Main Results:
- The alula increases lift and delays stall.
- Birds with the alula exhibit steeper descending flights and greater body orientation changes.
- A streamwise vortex generated by the alula suppresses flow separation and induces downwash.
Conclusions:
- The alula functions as a vortex generator.
- This vortex generation enhances lift and maneuverability at high angles of attack.
- Provides the first experimental evidence for the alula's vortex generator mechanism.
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