Hummingbird Flight: Two Vortex Trails With One Stroke

Feb. 25, 2013 — As of today (February 25), the Wikipedia entry for the hummingbird explains that the bird's flight generates in its wake a single trail of vortices that helps the bird hover. But after conducting experiments with hummingbirds in the lab, researchers at the University of California, Riverside propose that the hovering hummingbird instead produces two trails of vortices -- one under each wing per stroke -- that help generate the aerodynamic forces required for the bird to power and control its flight.

The results of the study could find wide application in aerospace technology and the development of unmanned vehicles for medical surveillance after natural disasters.

This cartoon shows the experimental setup.

 High-speed cameras recorded the hovering of

 hummingbirds in the lab. 

(Credit: Altshuler Lab, UC Riverside.)

The researchers used high-speed image sequences -- 500 frames per second -- of hummingbirds hover-feeding within a white plume (emitted by the heating of dry ice) to study the vortex wake from multiple perspectives. They also used particle image velocimetry (PIV), a flow-measuring method used in fluid mechanics, to quantitatively analyze the flow around the hummingbirds. PIV allowed the researchers to record the particles surrounding the birds and extract velocity fields.

The films and velocity fields showed two distinct jets of downwards airflow -- one under each wing of the hummingbird. They also revealed that vortex loops around each jet are shed during each upstroke and downstroke.

http://www.sciencedaily.com/releases/2013/02/130225153139.htm