To evaluate the influence of the velvet-like surface structure found on the suction side of barn owl wings on the flow field and on the aerodynamic performance of the wing, highspeed PIV and time-resolved force measurements were performed. Measurements were conducted in a Reynolds number range of 40,000 ≤ Re_c ≤ 120,000 based on the chord length and angles of attack of 0° ≤ α ≤ 6° for the PIV measurements and -15° ≤ α ≤ +20° for the force measurements, respectively. The clean wing model whose geometry corresponds to that of the owl wing without any special adaptations was investigated as a reference for the same range of Reynolds numbers and angles of attack. This clean wing possesses a laminar separation bubble as dominant flow feature. Two artificial surface structures were selected to mimic the natural surface concerning the length, density, and thickness of the filaments. The surfaces structures were able to reduce or even suppress flow separation. Although this reduction of the separation region might have a positive influence on the pressure drag of the wing, the aerodynamic performance of the models with the two artificial surfaces applied was significantly reduced due to the increased skin-friction drag. Nevertheless, it can be stated that the velvet surface stabilizes the flow field at low Reynolds numbers and as such the owl is able to fly more slowly and thus more silently.
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