The implications of low-speed fixed-wing aerofoil measurements on the analysis and performance of flapping bird wings
Author
Summary, in English
Bird flight occurs over a range of Reynolds numbers (Re; 104Re105, where Re is a measure of the relative importance of inertia and viscosity) that includes regimes where standard aerofoil performance is difficult to predict, compute or measure, with large performance jumps in response to small changes in geometry or environmental conditions. A comparison of measurements of fixed wing performance as a function of Re, combined with quantitative flow visualisation techniques, shows that, surprisingly, wakes of flapping bird wings at moderate flight speeds admit to certain simplifications where their basic properties can be understood through quasi-steady analysis. Indeed, a commonly cited measure of the relative flapping frequency, or wake unsteadiness, the Strouhal number, is seen to be approximately constant in accordance with a simple requirement for maintaining a moderate local angle of attack on the wing. Together, the measurements imply a fine control of boundary layer separation on the wings, with implications for control strategies and wing shape selection by natural and artificial fliers.
Publishing year
2008
Language
English
Pages
215-223
Publication/Series
Journal of Experimental Biology
Volume
211
Issue
2
Document type
Journal article
Publisher
The Company of Biologists Ltd
Topic
- Biological Sciences
Keywords
- animal flight
- aerofoil
- lift-drag polar
- wake analysis
- Reynolds number
Status
Published
Research group
- Animal Flight Lab
ISBN/ISSN/Other
- ISSN: 1477-9145