Abstract
A blower-type wind tunnel for physiological bird flight experiments has been developed, constructed and evaluated. Since the birds to be investigated are rather big (Northern Bald Ibis, Geronticus eremita), the cross-sectional area of the test section measures 2.5 m × 1.5 m. The maximum achievable flow speed is approximately 16 ms−1. The wind tunnel exhibits a flexible outlet nozzle to provide up- and downdraft to allow for gliding and climbing flights. The current paper describes in detail the layout, design and construction of the wind tunnel including its control. Numerical simulations of the flow and measurements of the velocity distribution in the test section are presented. Apart from a non-homogeneous flow region in the mixing layer at the boundaries of the free jet, the test section exhibits a very even velocity distribution; the local speed deviates by less than two percent from the mean velocity. The turbulence intensity inside the test section was measured to be between 1 and 2%. As a constraint, a limited budget was available for the project. Four northern bald ibises were hand-raised and trained to fly in the wind tunnel.
Highlights
Scientific experiments with flying birds can be performed when the birds are moving in their natural environment, namely in free air
Journal of Ornithology increase the bird’s required power to fly; it has been estimated that the added weight and increased drag of even small devices can decrease the flight range of small migrants significantly (Bowlin et al 2010)
The turbulence intensity is approximately 1% at the exit cross section and up to 2% at the end of the test section, which appears to be acceptable, though these are rather high values compared to wind tunnels specially designated for aerodynamic research
Summary
Scientific experiments with flying birds can be performed when the birds are moving in their natural environment, namely in free air. Journal of Ornithology increase the bird’s required power to fly; it has been estimated that the added weight and increased drag of even small devices can decrease the flight range of small migrants significantly (Bowlin et al 2010). An alternative approach is to change the frame of reference; not the bird and its equipment is moving in still air, but the air moves towards the bird with flight velocity—the bird appears stationary. This situation can be established using a wind tunnel. This paper deals with the latter, namely the development and construction of a wind tunnel for bird flight experiments. Since only a limited budget was available, many expensive components have been substituted by affordable alternatives, though without affecting the functionality of the final device
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