Meeting Abstract

21.4  Thursday, Jan. 3  The near-field flow generated by hummingbird wings WARRICK, D. R.*; TOBALSKE, B. W.; POWERS, D. R.; Oregon State Univ., Corvallis; University of Portland; George Fox University warrickd@science.oregonstate.edu

Hummingbirds, like other birds, generate lift coefficients far in excess (~ 2x) of those generated by typical man-made airfoils. The kinematic and Re number similarities between hummingbirds and large insects during hovering has lead to predictions that these animals should employ similar aerodynamic mechanisms. To reveal the flow characteristics responsible for lift generation, we measured the near-field (<5 mm from the surfaces of the wing) flow around the wings of hovering rufous hummingbirds (Selasphorus rufus, 3.3 g, n = 3) using digital particle image velocimetry (DPIV). We found no evidence of sustained, attached leading edge vorticity (LEV) during up or downstroke, as has been seen in similarly-sized insects – although there is some vorticity associated with the turbulent interface between boundary layers on the dorsal wing, and a transient LEV is produced during the rapid change in angle of attack at the end of the downstroke. The induced flow around the wing is so atypical as to render traditional measures of angle of attack meaningless, and the stagnation point for a hummingbird wing at mid-downstroke is on the ventral surface of the wing, far behind (~ 5mm, or 33% of wing chord) the leading edge. While rotational effects could theoretically account for some of the observed flow, kinematic data indicate little wing rotation at mid downstroke. Studies of pressure around a translating bird wing could address the possibility of compressible effects, and comparisons of Navier-Stokes computational fluid dynamics to actual near-field flow could reveal the adequacy of incompressible flow models in describing hummingbird flight. NSF IOB-0615648